I used that set-up for a bit. It did not work well with the 292/508 cam. I liked the look of it and really wanted it too work. Alas I had to pull it, in favor of a single diaphragm, which did work, and has continued to, since about year2000.
When I say it didn't work well, I mean because of the low idle vacuum of that cam it was slow to bring the booster on line.Building vacuum was not something that cam is known for. In fact I don't think that engine vacuum-peaked until over 2400 rpm,which woulda been 20mph in first;(I had a 4 speed with 3.55s and a 2.66 low). I always had to rev it up and charge the vacuum chamber, before backing off my yard. In traffic, it might lose it's charge, and I would find myself without boost.It seemed to have a high vacuum requirement.
It worked ok with a 270/280/110 cam. This cam vacuum-peaked much earlier and at a higher number.
That booster came off a 340 car, where it had been working just fine. The 340 cam was a 268/276/114