[Pete]

Your LB is a VERY poor engine to modify for more power. After market heads and manifolds can be found but are scarce and quite a bit more costly than parts for the 49-53 engines. The blocks can not be bored very much and crank bearings are way more expensive than the late ones. A far cheaper route to go, both initially and in the long run, would be to get a 49-53 Merc engine. It will bolt in with all stock parts and will make somewhat over 100 hp in stock form. You can modify it from there with readily available parts. A very mildly modified one will easily make 130 hp. and that is with a stock cam.