A 700R4 is a great tranny also. It's sorta like a 400 Turbo with overdrive is what I would say.
Thing is they are super expensive. My friend with a 67' Camaro just had one put in his car. The builder provided the trans. With the Transmission included, Labor, parts to build, etc. It cost old Marshall $1600 !!!
The best thing is he got what he wanted and its done right. Its your car so do what you want with it.
The truth though is go with a 400 Turbo depending on how much power you're going to have. The 350 Turbo is fine for a milder engine with less power.
Or the 700R4 if you want overdrive.