Like Andy said,there are lotsa' option's out there,I used '81 cordoba units on my 63 sport Fury,and on several later 68/69 RR's,but I'd turf the oem style pre '66 single pot m/cyl. my '62-64 Fury's have alway's been fine with 11" drums,I just grabbed a set of 11" drums from a '68 charger,that is in my shop for paint,my buddy doesn't want them,I'd rather bolt them on my '62 fury than the disc's, I bought a supply of NOS m/cyl's for a 66-67 belvedere years ago, and switched up to that dual reservoir,manual drum style m/cyl.with no booster,I think you should try a different set of shoes first,and let us know which master cyl. you are using,maybe you have a line or distribution valve blockage,bad wheel cyl. ??, could be something minor,the 11" should work with a lot less effort,,If you think you need it,I do have a '70 B body booster and manual master cyl. for drum brakes,kickin' around here someplace.