The place I had my spacers made is long gone but I'm sure there are lots of places that could make them. The specs I used were:
3/8" thick
ID (hub) 2.820"
OD 6.200"
1/32" chamfer on one or both sides of ID (the hub has a little radius to it)
I don't know what the ARP studs were, they were a standard item, maybe for Fords if I recall. You have to measure the knurl & figure it out. It's been a while since I did this, believe I disassembled the disc to press in the studs. If you don't put in the studs I'd be concerned, the stock ones will be on the short side & the strength less than the ARP. I generally don't like wheel spacers for safety reasons & the fact that they add additional force to the spindles but made an exception in this case.
If I were to do it again I'd just stick with the stock steel wheels & caps. Nice Chrysler disc brake covers for your car can be really hard to find though.