Look on the left side of the block above the starter this will tell you for sure. If it is a 318 with those X heads comp. will be pretty low unless they have been milled in which case you will have to mill your new intake to match
It's a 318 block, I have a funny feeling that the engine may be stroked and have a good bit of machine work done to it. It bugs me that the only way to know for sure is to tear it apart... She runs nice, sounds great, and definitely not at a loss for power.