I got this mystery head that had a mark on the combustion chamber that indicated something blew up in the bottom end. Cleaned up the mark. Now there's also one exhaust valve spring seat that obviously has been busted up. Problem is, it's not stock inner diameter. Exhaust valves on this head have a stem that's as thick as intakes. Any idea who made those? I just need ONE top spring retainer to make this otherwise good head work. Thanks in advance!