Joe, a lot of the Montagues that I have and have seen are often considered "mater stakes" by the bretheren of the boo. But other than the weight of them, some of them are pretty nice fishing rods. Now a lot of people call them "production rods" meaning that they were made on an assembly line and not by one skilled craftsmen.I would imagine that I have seen well over 200 Montagues altogether and a couple of things stand out in my mind about Monty's.
1. Most all of them never had a line weight written or stamped on them and the few that did came out of their custom rod shop.
2. They did use some of the best bamboo that money could buy at the time of production and you don't see very many Monty's with bad glue lines or bad bamboo in them.

Another thing that most people do not know is that Montague did make some of the Orvis Madison Blanks for Orvis many years ago. Rick Taupier, in Mass. (Swift River Fly Rods) knows a lot about Montague as he lives very close to where the old Monty plan was located.

If that old Monty is solid, and just needs a few guide on her, fix them and fish her.

You gave a little information about the taper but what you need to do is to mark the rod at intervals of 5" and take the readings with your mic or dial caliper and when you measure, measure across all three sets of flats and average them for each increment. When you get finished, you can compare the taper to those archived in Hexrod and get very close to a good educated guess on the weight of the line for the rod. Hex rod will also calculate and give you a stress curve that you can compare to archived tapers and that will give you some idea of the action the rod will have.

Make sure that you check the ferrules. Montague used plated brass ferrules for the most part and they are really bad to crack.

I agree with REE and JC, it will probably handle the 6 or the 7, and I like the Sylk lines. I use them almost exclusively now, even on my BIIx Winnie.