No crank machining required (unless your crank is bad). I would pull it and check for straightness and wear whilst you are in there. Also check the case for cracking and wear to the bearing saddles. Depending on mileage this is a good time to replace all bearings also to cope with the extra power. The only machining you will need to do is to open the case and heads for the 90.5's. Also worth re-machining the cylinder seating surfaces to ensure you have something flat to bolt them to. You will also need to check what your new compression ratio is, and correct if necessary - don't just bolt them on and assume everything is fine!
As a side note, make sure your supplier checks the new cylinders for concentricity - a surprising amount of them are out of round and/or not straight. Most suppliers don't check, as they can't return them either! Check he has a dial bore gauge, and knows how to use it!!
Good luck.
Al.
