The spacer I used was just a 1,5mm thick alu sheet that I cut to the shape of a base gasket. Remember the head has to be 'moved down' too, to keep the squish nice and tight. Can be done by machining the top of the cylinder down, or machining the head.
IMHO the head volume is too low from factory, and combustion chamber needs to be enlarged to have a safe CR if squish is below 1mm as I want it (0,8mm now). The 125 and 170 inserts seem to be the same from Athena..
No porting done on mine. I think widening the upper part of the exhaust could add some power at higher revs and keep the low band pretty much the same. Pretty easy to do a portmap on paper, but I did not do it before I installed the cylinder. Just measured the port height and calculated the port timings to get a rough idea what height I should try. Raising it the full 3mm to get the 'full opening' of the transfers gives pretty wild port timings, but it would probably work with custom ignition curve and pipe to make it a screamer (power at high revs). Not what I'm after though. Pretty happy with it as it is now.
