cb750F rear brake

Hey, I'm building a 750 chop, (well, it's already built and riding, but I'm re-building part of it) I got a honda 750 rear disc brake setup but don't know what year honda it would have came off of... The wheel is a laced (spoked) 18 inch and the caliper is a single piston
Can anyone tell me what year it came off of so i can get a rebuild kit for the caliper???  Thanks!
randy