I just picked up some GT 40 Aluminum heads and I'm looking to have them O-ringed at a local machine shop in prep for a turbo set up. Is o-ringing the heads a pretty standard process or will I be getting questions like what material and how tall of a ring do you want. I'd like to drop them off this weekend seeing as I'll be away from home for a while.

 

The o-ring in installed in the head gasket you use, like Fel Pro, so they shouldn't have any problem doing the heads as the rings are fairly standard sizes as far as I know.