My Roush 427 SR had
oil getting by the valve guides at 7k miles pulled the heads. Guides were fine, took heads to a the shop. The valve stems were worn. Come to find out they were cheap Chinese valves, and the valve guides had worn the valve stems allowing the
oil to flow. Fixed it pulled the engine and sold it, put a Keith Kraft 482 in it haven't regretted it one second. Just my experience. Know of one other member on here who had serious problems with his, but it's up to him if he wants to chime in. Just sayin