If you keep the ISO rear end hardware you will need to open up the holes in the perches so they fit the ISO stuff as it has a large locator pin.... I trashed all that stuff on my 74 RR put SS springs with the small locator pin, I used a 70 C-body rear that had 11 inch brakes. Cut off the old perches & had a race car shop weld new perches in the right spots and all is good...