Sorry, I misread your post, I was thinking you had a front drum/rear drum master cylinder. It sounds like you have the correct MC.
The front bowl/rear drum brake port uses a larger fitting on all of the dual reservoir master cylinders I've seen.
Here is a picture of the drum/drum MC from my '67 coupe, notice the size of the fitting on the front port. My '66 dual master cylinder Stainless Steel Brake system looks essentially the same. I don't know the exact size of these fittings, but I'm sure you can find an adapter at Napa. If you make up your own lines be conscious of the line size as well as the fitting size, I once bought lines with the correct fitting, but wrong I/D and they leaked horribly.
Good luck