Just thought I might add that the reason I asked in the first place about the heads is that tuning section here says that "only mc 18 s have truly center mounted plugs"
Well they dont! not mine anyway! Am I confused I dont Know? maybe i am reading it wrong
The MC28 HRC kit is nothing more than a stock top head and different radiator hose, although special heads were produced for all other models, with the 1988 and 1989 MC18's having true centre mounted plugs.

Cheers fastfill