My 48 business coupe has Omega (Nova) drum front and rear. These brakes are adequate for my ride.
But, saying that, I plan to upgrade to discs up front, already have the spindles. Discs will add 7/16 inch width on each side from the drum setup.
I'd think not having a proportioning valve would be a problem. It's been awhile since I did some research on this, but one or the other require quite a bit more pressure to activate, hence the proportioning valve.
You probably need to do a little more research on this issue, good luck upgrading the system.
Mike