You have the 3 valve pockets to increase the CR ratio, if you have 4 it means you have one valve pocket increasing the volume on the crown of the piston which will lower you CR ratio especially as it's the exhaust one which is bigger than the inlet valve pockets. Might only be a small decrease but with all the rest of the pockets not lining up you'd have to remachine them bigger anyways so your paying to have it done anyways and also you'll loose even more CR ratio because your increasing the volume on the dish of the piston. Having them made with blank crowns is much better they may even do it a bit cheaper. Failing that just get the Diamond ones and maybe ask them just to do 3 valve reliefs and have the rods re-bushes for 20mm pins which are lighter than 21mm but then 21mm are stronger if your running boost better off with 21mm or extreme rpm 21mm is better but if you can have titanium ones made that should help increase reliability.
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