That is a small port head that requires a lump on top of the piston to make compression. Often referred to as a 477 head.
A good deal for someone with a stock motor with a cracked head, but not a great head for a performance build.
The other small port head is the newer 819 head which can be milled 0.020 - 0.030 and used with flat top pistons to get 9:1 compression and with oversize valves and a little porting makes a decent performance head for a solid reliable driver.
