You may want to check and see if the m/c already has check valves internally. They'll be behind the inverted flare seats in the ports. The other thing to look at is piston diameter. Some m/c housings have that indicated on the outside of the m/c housing, e.g. 1 or 1 1/8". The larger the bore, the more pedal pressure you have to exert to activate the brakes. For drum/drum something like a 7/8" would be easier on the leg. Typically if the m/c was intended for power brakes it will have the larger bore.