I want to say that it was something like 1 1/2" spacer. I know from my experience with trying to make the late model GM stuff work that seems about right.
If you use the narrow REAR rotors off of an 03 and newer GM van it helps the spacer situation.
Just FYI here's a link to the Toms Classics bracket. It says 55-59, but the 52-59 trucks all use the same spindle.
https://www.ebay.com/itm/350973126802?item=350973126802&viewitem=&sspagename=ADME%3AX%3ARTQ%3AMOTORS%3A1123&vxp=mtr&rmvSB=true
