I honestly cant remember what i removed to get 11:1 - however whoever does the machine work should be able to measure/calculate for you.
As for piston size, +1mm was easily attainable, i believe you could go as far as +1.5mm (or maybe 1.25) but it was really not a good idea as the walls were getting v.thin at that point.
I ran +1mm pistons, decent compression, high lift solid cam, top spec head, fully balanced and blueprinted bottom end - would regularly hit 8k rpm on one of my old n/a cvh's - loved it!