Need opinion from those that KNOW.

I'm trying to replace my master cylinder. It's a manual, front and rear 10" drum setup..
My OEM M.C. has 2 equal reservoirs... I thought while doing brief research that 2 equal on the all 4 drum and a small and bigger combo reservoirs for disc. Inline Tube sales is trying to sell me the latter, the small front / larger second reservoir combo. Anyone know for sure..? Does it make a difference..? Also, he couldn't tell me if it was for 9" or 10" drums...which I thought made a difference.
T.I.A..
John