That's an interesting question. I don't really know the answer!
Looking at the TFSR manual,
tension assembly, it kind of looks like they may be interchanegable as long as you are switching out the entire assembly since there are more pieces and the "post" thing holds the spring a little differently.
While not actually taking them off an older 66 and newer 99 I have, they do look like they might be switched out, worth an experiment anyway!