Mine is like that also. It's a 6/70 with power brakes.Today we used 64 Impala (part# OER 3786368) speedo-cable grommet for our speedo cable. I've purchased several speedo cable grommets from several vendors only to find out the grommets are several mm larger than hole, not one fits, it's a 45mm+/- hole not a 52mm+/- hole. It was the only grommet not replaced since we bought it. I even bought solid body grommets to cut/drill but misplaced those. Btw it's a 6/70 build date but has qualities of a post 7/70
When I tried to buy brake parts years ago, SOR swore my tub had been changed, then a coworker bought one with very low miles and showed it to me. His was also 6/70 with 7/70 brakes.