<VV> master clyinder check valves

[rich dixon]

Question, When converting to a dual reserve brake master cylinder for my 66 coupe, how critical is it that the master cylinder have the check valve feature as the original? I purchased my part recently at my local parts store, and I assume that it does not have this feature. 
 
My question is basically, would is the down side of using a master cylinder that doesn't have the check valves. 
 
Thanks,
 
Rich 
Novi, MI