Pick any 12mm head bolt on the motor - you know, the generic 12mm head Mitsu bolt. I think it's an 8mm x 1.25, but it may be x 1.5. That's the proper stud thread for the head hole and the nut for the stud. L1 (the length in the head that's threaded) you can measure with a toothpic probe and a mm ruler. L2 (the part that sticks out) is manifold flange thickness + gasket + lock washer (relaxed total thickness) + flat washer + nut + about 3mm. Or go to Summit and buy the ARP studs. You need the Mitsu locking single use exhaust side locknuts, too. See other posts on cutting the webs of the exhaust manifold. Check the rear exh. mani bolt hole for stripping...