"Can you just redrill a 4 or 5cyl flywheel?"
Yes and no. A few years ago I had some time on my hands at work and modified a new 3500 flywheel. Two key differences exist when considering modifications to adapt it for use on the 4200. I say consider and cringe a little when I say that. If you want to spin something modified to 6500, it's your life and others that you must take responsibility for.
4200 vs 3500 pattern differences above
With that said, the two key differences are obviously the bolt pattern and the register bore ID plus ring gear offset. If you bore the 3500 flywheel to 4200 specs, you will bore into the existing holes. Looks like a mess. What I did is create some geometry just cutting beyond that bolt circle and make a alloy hub adapter. Lastly, the ring gear has to have the same offset from the mounting face and requires relocation.
online dice rollerLL8 to LLR/L52 Adapter
Modified 3500 Flywheel
Assembled together..match marked and bored for concintricity
Billet one piece with modified 3500
