Assuming that the manifold threads are clean, and the stud is new, none is probably required. If the stud is not plated, then I would put some anti-sieze compound on the stud. As I'm assembling my BJ8, anti-sieze goes on almost all threaded connections, even if nuts and bolts are new. The anti-sieze will mess up some torque values, I understand, so be careful there, but the application you're talking about is not a high torque situation. The only real reason to use any compound there is to ease removal, but that's an unlikely problem in the manifold. Especially since I'm sure your Healey will be treated with utmost care during its second life.