If you're talking making an Izzy kit correct for 30-06...then you need those 30-06 original specific parts which include barrel, barrel lock spring, booster, un-marked (for caliber) bolt, top cover, right rear cartridge stop. lock frame without screw adjustment and left plate pawl brackets. Probably a couple more parts I'm forgetting.
If you're talking making an Izzy kit compatible for shooting 30-06...then as toolmanm203 states, all you need do is install the 30-06 barrel / lock spring and pull the 308 feedway guides.
If you have the two piece booster/bearing then you can just swap the bearing when you change calibers which make it easy. It depends how far you want to go converting it back but if you are going back to pure USGI spec you will need to convert the belt holding pawl bracket and trunnion which the izzies altered, they made the cut for the belt holding pawl wider in both parts. They can be welded and reversed but it takes a bot of work.
A forum community dedicated to Browning 1919 A4 firearm owners and enthusiasts. Come join the discussion about performance, gunsmithing, restoration, troubleshooting, reviews, accessories, classifieds, and more!