Found a cylinder head while looking for other stuff, it has a 285 casting number. Think this could be an 70/71 MX head, the combustion chamber is pretty shallow compared to the 275? Head I have on the bike, the plugs lean toward the rear and there are 15 fins along the front. The 285 head has an overall different internal fin arrangement, 17 fins across the front and the two spark plug holes lean forward toward the front of the bike. I noticed on the '71 original sale brochure the plug seems to lean forward too. Anyone know what I have here? 

Not sure what you have but 285 is model code for "DT1CM" (motocross)

Sorry, casting # is a 284 not 5 . 

284 is model code for "RT1M"

Thanks for the info. What is your opinion on using the higher compression MX head v the stock head? Raising the compression, a bit more power? I always use VP race gas 110, so not too worried about pre-ignition or detonation.

Bad idea with Enduro RT cylinder porting.  It's already a high compression engine.