they sell f22b dohc heads in japan.... they are blue i believe ... you can find a f20b dohc or a f22b dohc... you might be able to find the head of it somewhere to do the conversion to DOHC with that... the head is the defining feature of the block's letter....
h heads fit on all h blocks, f heads fit on all f blocks, and b heads fit on all b blocks.... or at least thats what i was told