Just a WAG, but I believe (with no proof whatsoever) that there was only one wheel used for the space saver, P/N 9792737. This wheel was also used on the Chevelle and the Nova with N65. I can't find ANY info on the full size cars with 15" wheels and N65, but for the 14" wheel, it was probably the same 9792737. I also believe (again, without any proof whatsoever), that the Olds and Buick divisions used the same wheel. I KNOW Pontiac did since I found the information in the Pontiac P&A, so division-wide would make sense.
I'm also fairly certain the different ECLs were dependent on which tires were installed on the car (PL2, PL3, PL4, PL5, etc...). This would have dictated the tire size for the space saver, so different ECLs.
Ed