I have a 1990 RS V6 and am planning to go small block on it; hopefully GM ZZ383. What would be a good auto transmission that can handle 400+ HP and bolt into the car?

 

700r4

 

I'm not real familiar with the 700R4 but everyone I've ever worked on was garbage. Never really ever heard anyone say any thing good about them either. I don't know, maybe if I built the crap out of a 700 it might hold up...

Is there a Turbo 350 model that I can swap the tail housing off my 4L60 to?

 

You are an older guy? For those of us that where around in the 80's the 700R4 was a nightmare. I use to rebuild them and I hated them. But that information is dated. With the parts kits that are available today almost any trans shop can built a 700r4 that can handle a SB stroker. Even one for a 502 is just a kit. The only way I would do a 350 was if I was building the a 1/8 mile car and I was trailing it there. 700r4 has better first gear and Over drive. Heck even the 2004r is buildable these days. Back in the 80s they where considered V6 transmission.

Don't take my word for it. Go to a local car show, find some guys that have the 700r4 and ask who built it. I am sure there are some builders in your area, If you don't like that then shop online, give them a call. Search for reviews. Because of sites like this one performance companies that can not deliver on what they promise don't stay around long.