Listen to Kevin, he won't steer you in the wrong direction. To add what Burt Reynolds said though, you need to get totally commited to this build to get everything out of it. You need a bunch of stuff for everything to work at its potential. I'm not trying to scare you out of the 4mil, but rather giving you a heads up.
Things you will need in addition to your portwork:
4 mil crank, extra weld, and upgraded maxload bearings.
New seal kit.
You will need a new clutch, I would recomend the FAST clutch hands down.
Billet basket, I would put in new inner and outer clutch hubs as well, for $50 bucks why not.
Pancake bearing
You should go ahead and mod the transmisson parts while your in there.
You should also go ahead and let Kevin port match the cases.
Carbs, let Kevin help you decide on which carbs to run.
Intakes for the new carbs.
Filters for the new carbs.
Domes cut for the 4mil and new orings.
This list could go on for a while but I'm sure your getting the point. Once you get this list a little closer to completed your going to be very happy with your motor!