How to

[Wilkyinnh]

I have a 66 Chevelle that I purchased from someone who purchased it from someone who, well you get the idea. My question is this. I know that somewhere along the line the original motor was replaced with what I believe is a 350, but not really sure. I bought some supplies for a 1972 chevrolet 350 such as plugs, wires and the like, but the plug wire do not fit the distributor cap so I'm now wondering what I do have for a motor. Can someone give me an idea without pulling the heads and motor of how to identify what I have in the ole girl?
Really would appreciate it Also location on block will be helpful.