The idea of filling in the hollows at the ends of the brake lining to allow a much longer lining is also not new.
Norman,
Congratulations on providing another important product.
Phil Vincent was very careful to make sure that brake reliners could not screw up the complicated geometry of the lining placement. This is why he cast in the "dips" in the shoes. The dips forced the lining to form a 90 degree arc on the shoe. The angle is important, but having looked at the math many times I don't think there is a more complicated item on the bike than the brakes.
Because I do not understand the math I can only conclude that the 90 degree arc is a conservative choice for touring bike and is not necessarily chosen for maximum performance. I think this is fine. I use Japanese brakes and they have flat lining beds, so I have the same issue.
If you wish to have original Vincent style lining geometry it is fairly easy. Just tell the brake reliner to cut a 5.25" piece of lining and center it on the shoe. If you measure your linings and they are longer than you wish, just grind the lining back (there is no asbestos, but do it safely).
The standard for brake reliners is to line the entire lining bed and they expect the customer to "tune" the lining to suit by grinding. Most folks have no idea how to tune their linings, but racers usually do based on lots of trial and error.
The extra lining area does nothing. It may impair the brake performance. The Ferodo lads say this is so for a number of reasons. First, the lining needs to be mounted where the geometry works best to get the highest amount of servo action, not to get the most lining area. Second, the lining at the ends of the shoes is not able to grip the drum because there is no pressure at the extremes ends of the shoes. This can be seen clearly on the pivot ends which cannot move out toward the drum. Although the cam ends move, they don't move towards the drum. They move left and right. The center of pressure of the the shoe is near the center of the shoe. The forces look like this:
This is another reason it is difficult to get better performance by increasing the length of the lining. There just is not a lot of braking force happening there.
Third, and very important, the longer the lining the more clearance you have to adjust into the shoe. The Ferodo lads are very specific about this. The shorter the lining the less clearance you can run, so the shoe can be a hair of the drum. This generally works better for hand actuated brakes because of their limited travel.
I would offer the shoes with whatever lining your supplier deems useful. We know that the lining can be trimmed back a long way before getting to stock.
As for squeal, I use Triumph brake springs on the Japanese linings, just based on availability and fit. All your comments are right on point. One item that is not often thought of is that the lining itself wobbles around wildly when it is new and quite tall. This is why you need a long bevel to ease into the drum. The reason you never have to bevel a used lining is that as it wears it becomes much more stable. But, put a good bevel on when it is new.
One of the weak spots is the H48. The plate is too soft and maybe too thin. I made the decision to stick with the Japanese shoes for this reason only. The Japanese shoes have very thick hardened steel cast-in inserts.
The H48 is double thick on the one in the above photo, but I have found many like this:
With this type of detent worn in the brakes cannot work well. The cam falls into the detent and no more brake force to the drums. It is worth changing these at the first signs of deforming.
David