My question is this I have a body who is doing a drum to disk swap he bought an axcl o/o a 76 to put in his 72 now everyone recommends to use a newer master cylinder but other than the bore size I don't understand why dose the 72 have a check valve that would have to be removed, (I would think so) will it work, at least in the short term?
My 72 had the Mini-truck brakes on it when I bought it and my M/C looks the same as his I was thinking that mine still has the 72 M/C or maybe the other way around his already has a new one without a check valve and thats why his drums never worked quite right.
They both have plastic reservoirs, lines exit on the side, and pressure sensors or on the bottom
Any help would be appreciated.

The stock '72 master and booster will work just fine. That is the same setup I ran for years, with no problems at all.