The square tube that holds the tire mounting plate is adjustable. It can be slid in and out. Then, a nut and bolt secure it. Those threaded holes are so 2 more bolts can be threaded into them, so the tube doesn't rattle up and down. I ended up using different bolts than the Allen head cap screws shown in the photo.
'79 CJ5, AMC 360, t-18/d20 twin stick, dana 30/amc20(Mosers), Edelbrock Performer intake, Holley 600, ps/pb, DUI HEI, 'glass tub/1pc. tilt nose, 33x12.50 BFG AT's.
There's a fine line between "hobby" and "mental illness".