1971 master cylinder drum /drum looks like disc/drum

Hi I have a71 swinger 318 with 10 manual drums the master cylinder in the car looks like a disc drum combo with two different size reservoirs. I ordered a new one from Rock auto for drum drum 10" and it came big small reservoirs as well ?? what gives The 1970 listing for 10 drum was drum is adifferent number but picture shows both the same

..the disc drum master would have a larger reservoir for the front discs.
this is o.k. for drum/drum but you may need a residual pressure valve for the front depending on which wheel cylinders you have.
a residual valve is usually not installed in a disc reservoir due to pad drag.