We put a spectra in a 73 B Body 2 door. It fit, but the factory tank straps wouldn't make up with it. it was a situation where it was off just enough to not work. We bought the associated spectra straps and did not like them compared to the factory.

We wound up slightly modifying the factory straps and used longer J bolts to get the thing started and it finally went together. not a perfect fit, but 90%

I hadn't even realized they've been repopping in stainless, thanks for the info. Too bad there's nothing for my app - 74-76 B/440. CR21A is a regular steel tank Spectra makes for me but i sure do wish it was stainless. or even plastic