It's been about 35 years since I played with a Cleveland block, so a little rusty on info. However, the heads should have a 2 or 4 cast into the corner of the head somewhere if they are Clevelands. Could you have a 351M or 400? Here is a good site with lots of info:

http://home.comcast.net/~jelerath/mu.../specs-fr.html

Don