Th400 to standard transmission

[Feral Peasant]

Hey y'all I'm from the GMT400 forum but as of tomorrow I'll be buying a 1977 K20, it's basically a full roller no engine, th400 trans and no drive shafts. I'm looking to swap the th400 out for a standard transmission and I'm wondering what to go for.

I don't do too much if any off roading, I do a bit of highway driving, I'm planning to put a 350sbc in front of it with some things added for more power.

I know the NV4500 is popular for the gmt400s but I'm wondering if it's the same here, this would be my first project and manual vehicle so I don't really know much what I'm doing nor what is needed for the swap. I know I'll need the pedal but that's it lol.

 

[nvrenuf]

The sm465 4spd is the most common manual found in square (original or swapped) but that’s probably because they’re cheap compared to a 4500 and easier to plug & play.

The 4500 is probably the best choice and, if 32 spline, wouldn’t be difficult to adapt to the tcase behind your th400.

 

[bucket]

Yes, the nv4500 has been kinda the overdrive go-to here as well. As I'm sure you know, they are getting harder to find and are expensive though.

There's the rare overdrive 4 speed that was available in the 80's that would be a simple swap... but it is rare.

There's also a Tremec option if you want to use new parts. The swap cost would probably rival that of a used nv4500. (Once you install and drive the 4500, realize it has issues, then possibly overhaul it)

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The hydraulic style pedals have become very expensive. The older mechanical style clutch linkage setups are still fairly cheap though. If you are able to fabricate much, there are other options for building your own hydraulic setup with aftermarket parts or modifying what you have with a clutch pedal and some welding.