Not all that long ago there were 4 cylinder blocks on clearance for use with p5 head. If I recall correctly, they were less than $1000. Almost bought one, but that is one more project that I don’t need. At the time you could still get the raw cast version of the p5 head. Crank forgings for the 4 cylinder were also available. I would think a billet crank would be more what you would want though.
Didn’t “blofish” use a 4 cylinder p5 for a land speed record? It may have been a p7 headed 4. Don’t recall for sure.