I did some more experimenting today and downloaded a bundle of isolated vocals from the internet then set each useful one,
I loaded both versions into Melodyne and could see little differences between them.
As I could see, they sounds at the same tone.
I doubt that a visual in Melodyne will tell you much about the change in timbre.
Remember that Melodyne & other tuners reduce the vocal to a manageable size, (some sort of trickery with how low & high it places steep filters), to do their magic...effectively they are lossy processes.
Use your ears, experiment.
You're trying to do something that's, realistically, not likely to work.
You've been given that advise and some tools, in my case freebies, to address some of the issue.
Do you really think you've the experience to know Spec match isn't going to work for you after a quick go and a VISUAL cross check in Melodyne?
Changes can be subtle or aggressive, productive or destructive. I've been playing with it for a couple of hours and know that it can improve my voice - I want it to be subtle and I want to find the right profile for the right song. I'll keep looking & trying.
I suppose I should have added the caveats YMMV/YRMV.
Mate, if you want one click solutions you're in the wrong hobby/field.