Pre-'71, The boosters are different between drum and Disc. One being a dual diaphragm (disc) and the other a single diaphragm (drum). That being said, the power assist to pedal travel ratio is different between the two. Don't know the year of your car, but later 60's to about 1970 used a Bendix Booster for disc cars. They used a Midland booster for drum/drum cars. '71 on used a single diaphram "pancake" booster" for all. You should use the appropriate booster.
The Master cylinders are also different between disc and drum cars as well. Disc usually has a larger reservoir in the master than drum. Also, full on drum brakes will have residual valves in both the front and back reservoir ports (drum residual valves will not work on Disc's). You should use the appropriate booster.
Outside the booster/master, drum brake only cars have distribution valve/blocks. Disc brake cars have proportioning valves. A distribution valve just distributes brake fluid to the different circuits. A proportioning valve does the same, but it also limits the amount of pressure/fluid volume to circuits. In a disc/drum car, it would be limiting pressure to the drums. Again, you should use the appropriate valve.
Swaying off course from any of these when converting can adversely effect the vehicles braking performance, and quite possibly in a very drastic and dangerous manner. If you're converting to disc, do your research, don't cut corners, put together a well thought out & correct system, and you'll have a braking system that makes you wonder how in the heck you ever put up with drum's to begin with.
Good Luck
