I could be wrong here, but with a disc/drum setup I think you will need a proportioning/metering valve coming out of the mc. Since the discs are in contact with the rotors and the drums are not, this valve meters the correct force so as to keep the drums from locking up when braking.
Something like this
https://www.summitracing.com/parts/c...MaAufNEALw_wcB
It should come with a bracket to mount to the bottom of the MC or you could mount it near the radiator. It has two ports to the front discs and a single port for the rear drums.
On my truck, the rear line goes down the passenger side of the frame rail to a bracket (in front of the axle) where the steel line is mated with a flexible hose. The flexible hose then goes over the axle to another steel line which is then teed off to each drum.
Also FWIW, I just went down the route of attempting to flare my own lines. I made the mistake of buying stainless. It was a beast trying to flare those. I ended up punting and buying nickel copper lines with the fittings on them. it was much easier in the long run.