Have a 988 87A series apart doing and engine overhaul. Head is cracked at 4 of six precup threads. I believe this head is an aftermarket due to the fact it has no CAT casting #'s. The only meaningful # I can find is stamped in the top of the head in the cam shaft housing gasket surface at the left rear corner. It reads 0R2666. There is also NUDA stamped there. There were some other letters there but have been X'd out. Now........ I have what I believe to be an older head with a casting # of 8M100. It has the pre-heater tube running through the intake plennum. Question is will this head interchange. Physically it appears to be the same with the exception of the pre-heater tube. Any help is appreciated. Thanks. Steve.

That OR means it,s a Cat factory rebuilt (reconditioned) head that came from the factory and the other head sounds like it came from an engine that had a starting engine on it so it should work.