[weim55]

A few issues to take into account :

The input retainers will likely be different dimensions, This is the large round hole in the bell housing that centers the transmission. The aftermarket makes a sleeve that will convert the car Muncie four-speed to the larger truck bell housing hole.

Some of the car 4 speed Muncies Will have the Speedometer output on the passenger side which would need a longer cable to reach.

Car transmissions will not have the two lower holes that mount to the bell housing threaded as on the truck transmission. You’ll have to use a nut and bolt arrangement instead.

You will have to fab up A reverse light switch arrangement.

Probably have to make a drive shaft from scratch. Your original driveshaft will have a slip yoke in the shaft itself that won’t work on the car transmission.

The shifter can be a little tricky, but there are several solutions to clear the bench seat. I did the swap myself about 30 years ago and I used a 55-57 Chevrolet car Hurst shifter and it worked out well. That said depending on the transmission there are different mounting arrangements so not all shifters fit the same .

Other than that it’s pretty much a bolt in. One more thing to consider: if the trans you have is a real M21 ( very unlikely as these are very rare ) this will have a 2.20 first gear which would positively suck to drive in that truck, not a deep enough first gear. More likely you have the more common M 20 Which has a more livable 2.52 first gear.

Steve weim55 Colorado