Manual master cyl. question

[brads70]

I have manual brakes on my 70 Challenger with big disc conversion up front, drum on back. I'm wondering about replacing the master as everything else looks original and I'm going to replace the flex lines with the Russell braided ones. I assume someone has replaced it as car came with drums up front originally? When I bought the car it had 73-74 spindles with the smaller discs. How do I tell if the master is for discs and not the original drum set up? Master now is the one with the single bolt on lid, cast iron. I'm just thinking that maybe I should replace it all as I have no idea the age/condition of the brake components? Cheap insurance? No use going fast if you can't stop....with confidence?
What about this one ?
 http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&item=320430800100&ssPageName=STRK:MEWAX:IT




and what about this for the wheel cyl. out back? Any truth to the sellers description?
http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&item=220486822125&ssPageName=STRK:MEWAX:IT

[dodj]

I was told once that the master cylinder for cars with drums in the front have equal size reservoirs. I've never seen such a master cylinder on an e-body but I have on drum equipped b-bodies.
I replaced my master cylinder with one from the MP catalog, ordered it through the local dealer.

[Chryco Psycho]

the 70 disc master is as you describe , the real difference is the residual pressure valve in the master , the drum brakes use a 10 lb RP valve & will cause the discs to drag , discs either use no RP valve or they have a 2 lb
 I feel you can stick with what you have as long as the front discs are not dragging