Well hemi71x has just read this thread, and has a bit of time to kill this morning, before leaving for my medical appointment at the Mather VA.
In my experience in rebuilding these Kelsey Hayes 4 piston caliper, disc brake systems , on the A body line of cars, i once purchased a set up to rebuild, from a guy that raced at the track here in Sacramento.
I don't think your gonna find long whell studs 7/16 inch diameter thread size for those KH disc brakes anymore in this day and age.
Whats available works for Drum brakes and not discs.
Here's what i once did for long wheel studs, on the KH brakes.
I had my machine shop friend just drill the rotor and hub to a larger diameter to accept wheel studs from the 70 71 72 B & E body line of cars, with disc brakes.
The studs are then 1/2 inch diameter, but so what. You buy 1/2 inch lug nuts, to suit your application, and wheels.
Then long studs are pretty much findable for the 70 71 72 disc brake B & E body line of cars.
Well anyway, that's my 2 cents worth of reply to your posting.
Good luck.
Jim V.
hemi71x