I would try adjusting the valves 1st. The engine in my 89 was rebuilt with unknown miles. I have had it for about a year & it started knocking in the upper end only at high rpms. I removed the valve cover & found the valves were tight. I couldn't even get an .008" feeler gauge in the exhaust side. I adjusted them & the knock went away. This repair would have been free but it cost me the price of the valve cover gasket only cause it had been leaking
