Hello Dave,
Good choice with the TH350. Yes, all of the 3 speed automatics that we play with (TH400, 727, 904) are 1:1 ratio 3rds. If you wanted an overdriven transmission then you would have to look at 700R4, 200R4, 480LE etc. What camshaft are you running? Compression?

Cheers,
Alex