G’day D’man,
Valve sizes on the R17TS:
Inlet: 42.1mm
Exhaust: 35.35mm
No idea about the mangled spring seat washer but presumably that didn’t happen in service?
Before you start contemplating milling the head, I’d suggest you plan out your expectations.
I’m not sufficiently familiar with the 843 as used in the US but wasn’t it originally from a Fuego Turbo? I ask because if that’s the case, I’d suspect the stock compression to be somewhat low. Consequently, you’d end up skimming too much material from the head to get it up to something reasonable for a non-turbo.
As a first step it’s probably best to use JB’s method and discover the existing compression ratio.
It may well be that higher compression pistons and leaving the head alone is the way to go.
Yes, that groove looks to be an oil splash for the dizzy.
I’ve never seen discussions of problems arising from it’s disappearance, but it’d likely be a trivial job to re-cut a groove in a skimmed head.
As an aside, that 807-G4 engine is an 1800cc twin cam, 16valve, so it’s in a rather different league.