the machine shop will be able to check for flatness of the head, see if the valve seats need any attention, and look for any signs of wear and tear on the head that might need to be addressed. If you bring it to them and ask if they can inspect it they should be able to help you out. Just say you have a used head and you want to have it looked at before you throw it on your engine. If it's no good, they should be able to tell you and then you can look into your other options like clearwater.
88 YJ with a 4.6l stroker, AX-15, NP231, 2.5" lift, 4.10's and 33's
2000 Red XJ w/ 350k+, AW4, NP231, Locked Rear, HD Crown Leafs, trimmed to fit 33's, soon to be a donor
2000 Silver XJ, Drivetrain from the Red XJ, Stiffened, IRO leafs, RE coils, custom 3 link, WJ knuckles, 35's <=== In the works