Hi Joe... Just about every answer to any question regarding recording technique starts "Well, it all depends..." We have a lot more effects, etc. available to us now than we did back in the day.

So much of what they accomplished was through doing the simple things well. My best advice is listen to the vocal you want to copy - listen to it time and time and time again. I use headphones when I really want to pick something apart. Listen for vocal delay and reverb and slapback and doubling. They had great mics, live reverb rooms and Gotham plates...

Without going on for a few hours here, I'd also suggest you check out the Recording Revolution material on YouTube... You'll find a lot of great material there.

https://www.youtube.com/user/recordingrevolution

Regarding your purchase and use of the Helicon Voiceworks hardware box, I can't help you specifically with it as I
don't use pitch or vocal correction. It's not that I don't approve or like the tuning effects, I just haven't gone there - yet!

For success with vocals you'll need clean recordings: proper levels, sibilance control (de-essers) and light to medium amounts of compression/limiting...

Get that much right and then you can play with adding vocal "special effects" plugins all night long.

You may or may not want to follow this vocal chain:

The vocal mic (condenser or dynamic, it's all up to you and your wallet) placed 8-12 inches away from your mouth using a pop filter placed between the mic and your mouth...

It's best to hang the mic above your head pointing downward from above so your vocal plosives (b's, p's, etc.) are not being blown down directly into the mic - this is a lot easier to do with a large diaphragm mic like the Neumann U87,67,47, or their clones - or any mic designed to "hang" down from above.

If you can't manage the downward hanging thing with your current mic, try to "duck" your plosives by moving your mouth slightly to one side or the other as you sing a plosive into the mic. Always use a pop filter, buy one or make one. A Google search will give you several methods on how to make a pop filter.

The mic signal should then go into a stand-alone preamp if you have one (if not, your digital interface or board will provide the preamp duty).

Then I generally add a bit of compression or limiting to keep any signal clipping out of the picture before I put the signal "on tape".

Here in the digital age you must be sure you don't clip (overblown) the signal... These days I usually aim for the -12 neighborhood when tracking. (In the analog days we often red-lined all the way up to +3 on the 0VU meter scale going after tape saturation. It's been tough for me to lose that red-light mentality!!)

Other than the compression/limiting, I'd suggest you record the vocal signal "dry" without any other effects.

After you get a dry, dynamically-controlled and otherwise well-recorded vocal track "on tape", then you can experiment
with your effects as you seek to emulate the classic sounds.

The biggest mistake most fledgling engineers make is adding too much reverb, too much compression, too much whatever, etc... Long ago I was instructed by my boss to "set it where you think it's right, then back it down several clicks."

Regarding the classic Abba, the Beach Boys, the Bee Gees and Chicago recordings, I'm pretty sure they all used Gotham
EMT 140 plates as part of their vocal chain of effects - the plates were the standard vocal effect back in the day (if the studio had the space and the $$$)... As the art of recording progressed, compression, limiting, chorusing, flanging, etc. all came into the picture.

Some studios had live reverberation rooms/chambers back then - The Beach Boys and BeeGees recorded at both GoldStar and Capitol Records studios - both studios had great live reverb rooms that brought them a lot of business. Capitol still uses their live room(s) - actually they have 8 live rooms buried 20+' underground). They were designed/constructed by Les Paul in the early 50's and are still going strong.

Both plates and live rooms give the warm, dark reverberations to vocals that so many classic R&R tunes have... I love the sound. Of course the real deal sounds better, but the plug-ins are getting pretty damn good. And of course the "old fart factor" is in play here - things were always "better back in the day" - right?

Today there are some decent plate plugins out there both for sale and for free (I like the TAL Plate II - a VST freebie.) Regarding plate plugins... Play with the pre-delay amounts... and try rolling off the highs - I generally EQ shelf my plate returns to ban 1k and above... It's a matter of taste. Ask ten engineers a question and you'll get eleven answers...

Live doubling of vocals is a nice effect if your singer can do it... Brian Wilson was a master.

...or try duplicating your vocal track and sliding it 10-20 ms later than the original, then blend it back into the mix to fatten the vocal sound...

Parallel compression is a nice effect (make a duplicate track of your vocal and squash it mercilessly with compression, then blend it back into your mix with the original...)

Back in the late 50's and early 60's we used a lot of slapback echo on vocals by feeding a vocal track loop into a tape machine and routing the recorded, delayed signal back into the mix... The speed we ran the "slapback" machine at (1 7/8ips, 3 3/4ips or 7 1/2ips) determined to amount of vocal delay and "slap" fed back into the vocal effect return buss.

Many digital delay plug-ins have "slapback" simulations you might want to play with... (early Jerry Lee Lewis, Elvis,
right through to the 1970's Hollies' tune "Long Cool Woman" all used the slapback effect...)

I could go one here Joe, but I'm getting the feeling you asked me what time it was and I'm giving you directions on how to build an atomic clock.

So... most importantly get your vocal right at the source; then have at it with your effects plug-ins... and don't go overboard with the effects in the mix - unless that's your intention...

Good luck!

just an old analog dog tryin' to learn new tricks...