Took a couple of quick measurements on my 52 GMC 3/4 ton.
Inside backing plate to other backing plate is 51".
Center of tire tread to other tread center is about 58"
Spring center to spring center at the axle is about 26 3/4".
Don't have my wheel off at this time but could take more measurements later tonight if needed.
Misc info from my maintenance manual.
King pin length 5 5/8"
King pin diameter 0.9210" - 0.9214"
King pin hole ID 0.9217 - 0.9220"
