Can anyone tell me the differences,if any, between a RRA A2 upper for 9mm and the same for.223.

I know it doesnt have the gas tube hole, but are there any other changes, will a .223 bolt/carrier fit if I drill the gas tube holes.

I need to know so I either drill and build a 223 or buy new bolt/carrier etc and build a 9mm.
(or maybe a .38 super)mmm.

Thanks