Howdy James,
Are you local to Texas?
Welcome to the Texas Forum. I didn't check the Transmission Forum, but if you haven't posted there, I would suggest doing so to get a more robust set of opinions.
Tom has real world experience with two examples of C6 and echos an opinion of taller gears. Your 460 will have significant torque to spare to overcome the loss through a stock automatic. You might wish to investigate outcomes of changing axle ratio with rims/tires in mind.
Here is a link to a gear ratio calculator where you can alter various parameters to see gear/rpm/speed outcomes.
While all of the selectable transmissions in the calculator are manual, I suggest the newly added Quaife ZFQ Transaxle. This option will load with closest gear ratios to match a stock C6. First gear should be a pretty close match, your 2nd will be about half-way between the Quaife's 2nd and 3rd, and your 3rd will be a close match to Quaife's 4th.
Cheers and Welcome to the Texas Forum.
Please find other calculators under the reference tab on
my site.
John