> the tape would be pulled out the middle of the shell and put in a little isolated-loop drive
Transports to play Philips Compact Cassette tapes (loaded in-shell)
with a loop pulled outside the shell have been built.
> Better still would be a way to adjust the two pinchrollers so you could
> vary the tension/wrap on the heads.
Tension and wrap are never (intentionally) controlled by pinch
rollers. Where did you get that idea?
> Probably not worth rigging up such a beast for lowly cassettes.
Perhaps not in your world. But we have seen instances where missing
segments of original master tapes have been found only on the session
ATAE Studer / Audio Transfer Laboratory