Master cylinder replacement woes

I hate to be the bearer of bad news, but if the flare fittings are rounded off, even if you manage to break them loose you'll probably find that the brake line is also fused to the flare nut, ie, the tube will twist as you turn the nut.

Even if they don't, I'm assuming that the reason this bothers you is that you're planning on re-using the old brake lines. Since the flare fittings are already round, you're going to have to replace them anyway, you probably won't be able to get them tight enough again to keep them from leaking. Which means you're already into cutting the lines to replace the flare fittings.

I recently converted a '55 Dodge Coronet over to a dual master cylinder.It ended up being a bigger job than I thought it would be too, I made all new brake lines for it. This wasn't just because of the ancient frozen brake lines though. I'm not sure how your brake block is designed, but since there was only chamber in the master cylinder, I'm guessing there's only 1 input. Which means that the once in the block, the front and rear lines are no longer separate systems. So, you can't "T" the two inputs from the dual master into each other without totally defeating the purpose of having a dual master, one leak would still empty both chambers.

So, I guess what I'm saying is that even if the old brake lines were in good condition, you probably won't be able to use the old lines with a new brake block anyway, and (more than likely) you'll need a new block to make this work properly, one that keeps the front and rear brake lines as separate systems.

I used a brake block off of a '71 Dodge Dart with 4 wheel drums (go figure, I had one). I made up the new lines using the old lines as a pattern, except for the changes needed for the new block (different mounting location). You'll also need to include a brake light pressure switch somewhere in the system, I'm guessing your old single chamber master cylinder had it as an integral part (the '55 did, and they really didn't change them much). So you'll have to plumb that in too.