There is a system that piggybacks a dual master to the output of the original master cylinder. It seems to have too many moving parts for my piece of mind, but a system like that is out there.
I know one of the parts carriers had a 2 chamber master for my 1940, but the catch was it would not accomodate a clutch, so an automatic transmission had to be used. The 38 and 40 should have a very similar brake and clutch setup with the brake and clutch pedals mounting to the transmission and bellhousing.
