Jay,
How the heck do you change the bore centers on a block? Is the change so small it makes no difference at the crank? Where would you get heads to sit over the bores?
The trick is in the pistons. You have to have enough room between the pin bosses so that the rod can slide over on the pin, to compensate for the bores being off center. So, with the SOHC's block, the inboard bores are moved outboard 0.035", and the outboard bores are moved out 0.105". That's not really that much, so making the rods fit the pistons wasn't a big deal.
The piston dome is a little tougher; basically the dome has to match up to the heads. So all the pistons in the engine have offset domes. The bore is so large that there is room to do that, and the SOHC chamber is only about 4.1" in diameter, so wth the larger bore there was room to move the piston dome.
The pistons are expensive, but running a really big bore has a lot of benefits, including more cubes and more room for the valves to breathe.
