Whats the difference between the La and the FP OS heads is the bolt pattern the same or not even close thanks

The FP has 6 bolts and the LA has 4, why do you ask?

I have never paid much attention to them and have owned quite a few i have a new RJL diesel head but gave all FPs away a couple years ago and was looking for one to dieselize thought the la head was the same but i can see now its not. guess i will try to trade my OS 40 La in on one if i can find a trade thanks for the info

The FP and FSR heads are a match also in the 40 size.

FP heads are circular . LA heads are a squarer shape with rounded corners.

The two are completely different

Most diesel conversion heads for LA's are round also. They look unusual when mounted on the LA crankcase.