I have a 6 lug disc conversion for the early straight axle (passenger car).  It is from ABS power brakes in California.  here is their listing:

#411 1938-40 Chevrolet Car 6 Lug Front Disc Brake Kit.

I do not have the master cylinder or the master cylinder mount or the brake hoses.  It has rotors, bearings, brackets, calipers.  I ran the thing about 30 miles but it didnt fit my wheel offset.   $400 and  Ill cover shipping in the US of A.  (shipping cost me over $100).  Contact me with questions or pictures.