Hi David and welcome. As a guest member you will not be able to post a picture and your first few posts will be moderated so will not appear immediately. You will also only have access for 90 days.
I used to have a 49 G80. The original cylinderhead would be iron not aluminium. Under the rocker box would be hairspring rather than coil springs. There would be 4 holes for head bolts, two holes for the valve stems and two further holes on the timing side for the pushrods. The hole for the sparkplug is outside the rockerbox. A hole burnt through the head seems unlikely but i gues possible if special fuel was being used. I would have thought it obvious if this was the damage. The 350 and 500 heads look very similar and can be diffentiated by the inlet valve. On the 500 these are the same size as the exhaust valve on the 350 head they are smaller. The exhaust pipe is smaller on the 350 too.
I think you may find any combination of parts on your bike as much of it could be transferred year to year and engines may have been uprated especially if used for racing. So the starting point is your cylinderhead aluminium or iron. A magnet will tell you. Incidentally the set up for an aluminium head is similar in terms of the holes.
Regards
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Cylinder Head Question
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- clive
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