Pros an Cons: SBP v LBP

One thing I didnt see mentioned in the parts needed is the combination valve. Yes he will have to change out the master cylinder (drum/drum is equal size, drum/disk is a bigger reservoir on one side than the other in the master cylinder) which is easy to get at Napa, etc., but he will also have to change out the combination valve, wont he? Otherwise the proportioning will be for all drums instead of drum/ disk, which keeps the drums from locking up first. I think Inline is the only place I have heard people say has the valve - I know Napa doesnt have it cause I asked them for it to use in my changeover. Unless someone knows different?