I'm new to the forums and new to the more technical aspects of car repair/upgrade. So please forgive me for my ignorance and if these questions have been asked on these boards before.

Okay, number one: my engine (see more info about it below) has an Edelbrock performer series intake manifold on it. On it resides a carb that does not fit the intake proberly nor is it set up properly. I have decided to replace it with an Edelbrock performer series carb. I have'nt ordered the new carb yet, because I'm not sure whether I need a a spread-bore or a square-bore carb. I have'nt removed the old carb yet, so my question is when I remove the carb, how do I know which bore type it is? What's the difference between square & spread bore?

Also, the engine in my Jag is supposedly from a '74 Chevy pickup. I wanna know though how do I tell if it's a big block or small block, what's the difference between big and small block?

Thanks in advance guys.