I read about and checked out your 37 when I first found the CHR site. That's going to be a bad Mofo,...or Mopar. I'm going a little milder than you and using an injected 318 and the big overdrive (A 518?) trans. and lock up converter.
When I get the ft. completed with the new 11" discs rolling I'm going to install the rear brakes & seal that end up. I'll get some pics of the mounts and shackles.
I like the D-50 springs cause 1 they are Dodge, 2 the length from the rear shackle to axel center is same as the 35, 3 the front part is short and makes me think they won't flex much under acceleration (any feed back on #3), and 4 the trucks have similiar weight.
Kerry