my opinion...700R4 since you already have open driveline.....I ended up putting the 700 in both my vehicles after trying the 350 tranny.

.....and maybe a rearend from a Malibu, Monte Carlo, some olds and others.

1937 Chevy Pickup
In the Gallery
1952 Chevy Panel
In the Gallery
More photos
1950 Chevy Coupe
Pictures!

I'd rather walk and carry a Chevy hub cap than ride in a Ferd.
I can explain it to you, but I can't understand it for you smile