The issue with Ultima engines is that they where using ross pistons and they had issue's with either piston growth there lack of in the bottom of the bore, or cylinder expanding to fast. They addressed it by using a Mahl piston. The 127 is the largest that will fit in a stock frame,( some times they will not due to frame varance) but even at that you must pull the engine to service the rocker boxes. The 127 has a better compression ratio than the 120, the heads have HUGE chambers 99-103 and there is almost nothing to mill off the surface. best thing if you want one is to buy it as a kit toss the pistons use some dome pistons, and run from there or swap out the cams. But the engine is made of mostly overseas parts, The heads, cylinders, crank, cases, rocker boxes, are all import items. For the money and having run them I would buy a REV tech ( did I say that out loud??) but the new GenIII CC engines are backed with one heck of a warranty and they will take care of it without any issue. Not so with the Ultima. We waited 5 weeks for new pistons and cylinders.