Newbie, problems, and lots of good questions

Well, where to begin? I just picked up a 09/84 b2000, running great when i got it, but now it is making a loud knocking noise from my number 3 piston when I give it any gas, the noise isnt constant though, pretty much only while it is increasing in RPM's. when it levels at an RPM it stops knocking. When i disconnect the spark plug from the number 3 cylinder it stops making the noise too. If it helps it is the chain drivin 2.0 engine. My questions are:

1. Would I be able to swap to a belt drive?
2. What could that knocking be?
I am going to end up rebuilding the engine so any useful tips will help!!

I took off the oil pan and sure enough, my number the rod is twisted. I ordered the rod and piston with a set of rod bearings. Good old head gasket fun.