It takes a 101mm stroker kit and a bore of 86mm to reach 3.5l.... and the cylinder walls are as thin as you could safely go. You can't reach 3.5l without a stroker kit.
http://www.supramania.com/forums/showthread.php?t=62953
With a stock stroke of 91mm you'd need a bore of 91mm... you'd be able to see through the walls at 87mm.