what m/c to use

have a leaky m/c on my 72 demon. car is 340/727, man disc brakes. the m/c
i'm taking off has big & small reservoirs. put a small/small res. on. which parts
store gave me. brakes don't seem to work as well. need 4 bolt pattern m/c.
can i upgrade to diff year? they ordered a 3rd m/c today. have tomorrow.
any suggs.? don't want to modify parts. thanks.
jerry