1985 C10 2wd Swapped Engine/Trans Identification

[SKarpenz]

Hey guys, I picked this beast up for $500 from a family friend a few weeks ago.



Its an 85 C10 w/ no major rust (body or frame) just some minor surface rust. It definitely needs some work, but I bought it for a project, so its all good.

My problem lies here, I have never owned a carb'd vehicle, or a chevy V8 at that, and the truck was originally a 4.3 V6 (according to the markings and decals under the hood). Well right now it has a small block V8, and I'm betting on 305, but I'm not sure how to identify one from the other since the 305/350 blocks are the same dimensions and whatnot. Can anyone help me here?

Also, it has a manual transmission which is SHOT and needs replacement but I'm not sure how to identify that either. I can't even come to a conclusion on how many gears it has, much less decode casting marks or serial numbers.

Right now it has a holley 4bbl carb, holley street dominator manifold, and long tube headers. I have more plans, but mainly for paint/body not performance. It is just bugging me not knowing exactly whats under the hood.

Can anyone point me in the right direction?