67 brake booster swap out

[Chevystep]

Hey fellers, going to swap out my 66 single reservoir master cylinder for a 67 dual reservoir master to at least have some backup if one fails. Sticking with the original drums, can any of you 67 owners tell me if the dual master will swap out to the same bolt pattern? Here's a pict or two of my original setup and firewall stud location. Center to center on the bolt pattern is 3.5"... Sorry if the picts are head twisters...you get the idea..I know I'll probably have to modify the pushrod...Thanks!