Picked up entire GL-10 rear suspension today, ran the loyale up on ramps a climbed under for a look.. I was most worried about the brake hardware routing and how to plumb in the GL-10 proportioning valve.
The Loyale is exactly the same, but for the drum brakes, already has proportioning valve plumbed in. Now, either the valves look the same but differ internally, or the GL-10 must have a different master cylinder, but I can't get a straight answer on the subject, including from Subaru.
So, here is plan. Will replace the Loyale bits with the GL-10 bits, but for the proportioning valve, and see if rears tend to lock up. If so, will replace Loyale MC with GL-10 part, and try again. If this fixes the problem, the MCs are different. If it doesn't fix the problem, will replace Loyale proportioning valve with identical-looking part from GL-10. If that fixes the problem, it's the valve.
Gonna need gallons of brake fluid..