Yep, I literally just bled the brakes on my 65 Skylark this morning with 72 Olds Cutless (any A body, Skylark, Chevelle, Tempest, Cutless) Disc brakes bolted on, complete spindle. Then complete brake master with brackets and hard lines going to the proportioning valve all off the same 72 Cutless.
On the same note, if all you are after is eliminating the single reservoir for safety reasons, the other angle is to simply rebuild it all and drive it keeping it well maintained.
My daily driver has a single reservoir master cyl and I don't think a thing of it. I was all replaced new, lines and all because it had been parked a long time. But With it all new, just like the millions of cars that drove the roads for years like this. If you let a system go, if you don't do your brakes properly or of course there is the chance of some freak accident something flying up and damaging a brake line or hose, but other than that, they work fine.
But you could pickup the 67 dual master cyl and bolt it right on, running your drum brakes that work fine. Run new hard lines down and putting a junction block for the rear line to go into then for a new one to come down to it. On the front same thing, it could be done in an afternoon. And a real parts store is going to have all this stuff in stock. The new brake lines that have a dark greenish finish on them bend real easy without kinking, they are super easy to work with if you don't have a bender.
You simply bend them over something kinda round with your old one to compare it to. It is VERY easy, and they come in many different lengths so you will likely not have to do any double flares at the end or anything. If there isn't an exact length you can often make one with the combination of a couple of the pre-made ones with a coupler in the middle. Or if it's a little too long you can make a loop in it or just make a few extra bends to take up a little length, it will all work exactly the same.
Honestly, you could do this in an afternoon it is no big deal.