The only dumb question is the one you don't ask. Greetings. When you remove the carburetor, look at the mounting on the manifold. If it is square with four holes the same size, then it is a square bore. If the two rear holes are way bigger than the front ones, then it is a spread bore.

If the engine in your Jag is a 350, then it is a small block. You can tell by looking at the valve covers. A small block valve cover is held on at four mounting points--two on each side. Big blocks have more.