I'm looking at buying a 73 shovel with an S&S engine, I'm not sure what size the engine is or how old it is, the problem is that it is missing the rear head. how someone loses a head is beyond me but it happened, the part number on the front head is 90-1020f and i can't find any info on these anywhere on the net. i don't recall the full part number on the cylinders but i do know it ended in -80 does this mean it's an 80 incher? any info on this engine or where to buy a rear head would be great!!!