im looking at buying a 75 jimmy with a 6 cylinder and a 3-speed on the tree. If I buy it i'd like to keep the 3-speed, but swap in a v-8. Will the tranny hold up or should I go to a 4-speed?

 

The transmission will hold up fine behind a v8, but it can be a pain. The linkage for the 3-on-the-tree can cause problems.

 

I didn't even know the GM put the old I6 in the K5's. I'd keep the engine because those things are bullet proof AND cool!

 

Yep, there were two I6 engines offered in the 2nd gen trucks. The '74 Jimmy I'll be picking up in the spring (rusted out bad) has the I6 engine, but I am not sure if it is the 250cid or the larger 292cid (thought I knew, but the pictures I have on my cell phone suck!). It mated up to what I believe to be an SM465 and NP205 transfer case.