I went out today and followed your suggestions. Just balancing one reel and swapping out lines saves a bunch of fiddling around for sure! I started with a 5wt and it felt too light with very little loading. Put on a 6wt and it felt a lot better and was loading the rod nicely. I didn’t have a 7wt floating line but I had an intermediate I fish a lot for larger fish in shallow water. I have to admit, having never cast bamboo before it was a very different feel and somewhat awkward with the 5 & 6 wt lines. The 7wt int. was like I had been using that rod most of my life, it was butter smooth, with nice loops and it loaded beautifully.For testing tie on an older heavy fly reel and try the balance. It should balance close to the nose of the grip or within an inch or two of the end of it. Once you find the right reel you can use any reel and line weight you have on hand, lay the testing line reel on the ground and peel off 50' of line. Thread the rod and see how it feels. Then do the same with any other reel and line you have. That way the rod is balanced, and you don't have to respool fly lines for testing. I'd start with a 5 and work my way up. Slow your stroke down and let the rod load and do the work.
It is true that bamboo fly rods are sensitive to line tapers, and also manufacturers. I have come to like the 406 fly lines out of Montana to fit my rods and casting style. You might even be able to go to a 6wt line from a different taper or manufacturer. Buth there is nothing wrong with tossing a 7WT if that is what feels good.I’d guess 80-90% of the older Monty’s 8-1/2’ will be a six weight, maybe an even higher. But sometimes bamboo rods get picky even within a “line weight” with some wanting a more aggressive or more gentle taper, which is not a very technical way to say that. So once you find the right line weight, you might find another line in the same weight that works even better with that rods taper. It’s part of the fun if you want to look into that rabbit hole.
Mike, 406 is the one line that seems to work well on the most rods. I don’t know why that is but otherwise picky bamboo rods all seem to agree on those 406 lines.It is true that bamboo fly rods are sensitive to line tapers, and also manufacturers. I have come to like the 406 fly lines out of Montana to fit my rods and casting style. You might even be able to go to a 6wt line from a different taper or manufacturer. Buth there is nothing wrong with tossing a 7WT if that is what feels good.