If you are planning on switching to a rail vs the plastic base guard I would just spend the $150 now. These uppers require a rail that fits around the gas block so they are very size specific. Because of this design requirement there are only so many brands that even make them. They also are limited on barrel nut design due to the piston bar design that Adams Arms uses. I have not seen what the barrel nut looks like under the base versions handguard but if it is not the same it would have to be removed and replaced. So then you would need an armorers wrench if you do not have one already or pay someone to do it if no one you know can do it for you.