I think the only problem you may run into is that at some point the T-5s went to electronic speedos, I think '88. If you use a later tranny you would have to use aftermarket guages or spend $200 - $300 dollars for an electrical-mechanical conversion unit.

'51 Chevy 1/2 ton w/'62 261, HEI, offy, fentons, dual carter/webbers, t-5 & 12 bolt posi