If you don't get a response in a few days, try PM to Mastershake - he may not look in this forum as much as Restoration and General Q&A.If
the photos of the Dorman's are accurate, yes the large resevoir indicates both should be for Front Disk, Rear Drum.
Generally the drum brakes will have a residual valve in the master cylinder outlet. http://www.imperialclub.org/Repair/Lit/Master/274/page04.htm
This is because the springs on the shoes force the brake fluid back into the m/c. (Some later models moved the location of those valves)
According the Mopar Action chart, '71 B-body disk system used the same master cylinder for Power and Manual.
I can see why it seems from the Summit info that they are the same; something there may be wrong.
Need a '71 Service manual to see if there was any differences in Bore and Stroke inside the Drum M/C to Disk M/C for your Bee. If not, what aftermarket sometimes does is sell Drum brake MC for disk brake applications by simply removing the residual valve in the rear (front brake) outlet. Technically they work; but the rear resevoir needs topping off as the front pads wear.