Definately a 235 or 261 would bolt right in.
On the 4 speed, you could go with an SM420. They were used all the way up until 1966 and even into the 80's in some of the bigger trucks and military rigs. They came with both options, open or closed driveline, so all you need to do is find the adapter and yoke for the closed driveline and your set.
Jeff
