No one said anything about what is in the T-Bird now (352 or 430). These are all Ford big blocks & an power upgrade to a1966 or later 428 Ford block would be nice. Has anyone considered issues with motor mount, transmission & linkage or drive shaft??
Personally, my current Fords are 64 & 65 TBird convs, 63 Galaxie XL 2dr, 69 Mustang conv & retro 2004 T-Bird, - I would hate to change the power train from Ford on any of them. And I'm the same on my 72 Mopar gold Duster, 2005 supercharged Crossfire SRT conv, & my supercharged Pontiac Grand Prix GTP.
I bought & like each of these cars for what they brought to the table in their own time. While I've upgraded a number of common sense performance areas on some, I've kept each car generally true to the manufacture who designed & made them, without my being a "every original nut & bolt" fanatic. So I guess I would suggest keeping a "Vintage 1960 T-Bird" true to "FoMoCo".