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@gbj_tester
Ergal made in the 70s/80s should be pretty strong by now :-)
They had a reputation for being super "soft" (low yield strength) when new, I'm guessing they used 7075-0 alloy for extrusion and bending into hoops and didn't do any post-forming heat treatment. In the absence of any other degradation processes, many aluminium alloys which were not artificially aged at birth get stronger as they get older. If you don't artificially age, yield strength can double in the first few days after quenching, so with no factory heat treatment the rims would have gone to wheelbuilders in roughly the T4 condition. The ageing process slows down exponentially (and can be slowed even more or even completely halted by storing at low temperature), so life may be too short to get to T6 condition by ageing at room temperature, but in 20-30 years the strength could probably go up meaningfully towards the roughly double strength which artificial ageing can achieve over material which is naturally aged for only a few days.