Greetings and welcome to the forum.
I did a similar engine swap on my 1962 C10. I have the sm420 4 speed. I went from the 235 straight 6, to the 327 V8. My "new" engine was out of a 1967 passenger car and the bolt pattern was the same as the 235 so no changes were required for the bellhousing. The clutch is actually easier since we have the hydraulic clutches, just keep the line routed across the top of the bellhousing and it will be fine.
One thing you will also need to consider is the throttle linkage. For the 235, the linkage comes out of the firewall and the arm points down. This is so it can 'push' the linkage on the side of the 235. For the V8's, it comes out of the firewall and the arm points up so it can 'pull' the throttle on the carb. I took the easy route and swapped out the entire linkage as a unit from a junkyard donor truck. There are just 2 bolts under the dash that hold it to the firewall.
The engine mounts are another issue. 1960 - 1962 frames are shorter in cross section than the 1963 - 1966 (perhaps later)frames were. There are V8 mounts for the 60-62, but they are few and far between, so how I handled that was to use 1963-66 engine mounts and a spacer to make up the difference.
My frame had holes already drilled in the frame, but not in the crossmember, for the V8 mounts, so I mounted them to the engine and installed it in the truck, hooked up the two bottom bolts on the tranny, and put bolts into the top (frame) holes of the motor mount. I then marked the crossmember and pulled the engine out.
Next I drilled the crossmember for the lower holes and reinstalled the engine.
Your original exhaust will not work so you will need to replace/modify that as well.
I hope this helps you a bit.
