Super Turbine 300 to a TH350 or TH400 swap

[Hurricanes7]

Does anyone know if this is a direct replacement the way the powerglide swap to a TH350 is? I thought I had a powerglide but after more research and looking under the car, it's a Super Turbine 300. I want to replace it with a TH350. In a prior post I was searching for the engine size of my 67 Firebird, now I do believe it's a 400. Or since it's a 400 engine, would a TH400 tranny be better. I do not plan on building up the engine other then putting on an Edelbrock manifold, new carb and maybe some headers.

[hotrod_chevyz]

A 400 transmission requires a 400 driveshaft to transmission connection, and a $30 u-joint, as well as a detent switch located at the throttle for *drop down*. I would say if the transmission in it works *if it aint broke dont fix it*. If your doing it for a performance mod, i wouldnt bother. Gearing it up, bumping up the compression, or putting a cam in it would be a better Mod. If your looking for RWHP, them simply put a rock crusher in it, with a kevlar compound clutch. Any auto transmission kills some RWHP, but still gets a more consistent trap time.

T