OK...your Choate stock will do fine...your going to need to swap out the magnum bolt head for a .473 bolt head...your long action will feed the .308 parent cartridge .243 just fine HOWEVER your CDI DBM will need t be swapped out for a bottom metal for the 308 size cartridge...no way around it...the .243 will probably rattle around in that mag if you tried to mod it...call CDI and they'll hook you up...I'm kinda in a similar situation as I have an older 110 action built as a GSR (guerrilla sniper rifle) in .308...I just traded a crap load of 300WM ammo I'll never shoot again (shoulders) for a nearly new 26" Bull Stainless barrel in .243AI...so I'm good to go...the longer bottom metal is going to be your biggest hurdle...

Capt Beach