As far as the valve specs go, call a Honda service place and get clearances for the B18C head that you're using. As far as the OBD stuff goes, if you want it to be 49 or 50 state legal, make sure that all the emissions equipment for the cylinder head that you're using is hooked up. I say the cylinder head (as opposed to the block) becuz youre buiding a frankenstein engine, which is already gonna get you into trouble at a smog station, and the head has alll of the emissions stuff on it. The only thing the block has is the oil pressure sender, if I remember correctly. Soooo, if you make sure the head follows emissions specs for the year it was made, you should be able to get away with the block.