Just messing around with the idea of putting 15" rims onto my '46 Special to get it sitting a bit lower.
The fronts will be not much of a problem, as I would be fitting up disc brakes at the same time, allowing me clearance between caliper and rim.
Unfortunately,the rear drums hang up on the rims because the bump on the outside edge of the drum interferes. I don't want to machine anything on either the wheel or the drum.
Does anybody know if there is a smaller diameter drum with a 5 on 5.5 pattern that would be OK to use.? Something that matched the mounting holes would be ideal, (is that too ambitious).
I'm leaving the torque tube in it for the forseeable future, so I need to adapt to that.

I put 15" wheels on my 38 Special, the 38 Century came with 15" wheels. I thought the drums were the same both the 38 & 46 Special's have 12" brakes. Should be a 5 on 5 bolt pattern. The wheels I used were from US WHEEL they were the only ones that had a big center hole.

My mistake. You're correct about the stud pattern.
Still leaves me with the clearance problem for my wheels.
What, if any, buick or GM models run an 11" or even a 10" run setup on the rear?
Downsizing my rear drums may also help with being overbraked when I come to fit discs on the front.

I have 12" drums on mine and the 15" wheels fit no problem front and back.

I have an Australian built 46 special, and most of a 48 special sitting in the paddock. The 48 has smaller wider drums than the 46. It is nearly midnight here in Western Australia, but I will go out and measure the diameter of each drum if you think it might help.

Maybe that's the problem, as I am in Oz with an Australian built Special also.
If you don't mind having a look at your 48 that would help. I don't suppose that you could also see if it looks like the 48 drum is the same fitment to the diff housing as 46.
Thanks.