hieronymous -
If I remember my Cheap Trick trivia properly, the 12-string basses didn't show up on records until Budokan. The 3 records that were before that were Thunderbird and Jazz basses and an Alembic 8-string. It really sounds very Alembic on In Color. The switch to Hamer 12-strings was fully in place on Heaven Tonight.
Another interesting Tom Petersson trivia... Modulus made a lot of unusual custom instruments and my 12-string bass isn't even in the top echelon. But I think the most insane instrument they ever built was an 18-string bass. This was tuned like a guitar an octave down x 3 (so low E, instead of low B). Giant flat neck like an aircraft carrier, gazillion tuner headstock, and giant long custom Bartolini pickups. This instrument was built for Tom Petersson and kind of disappeared for more than a decade. It resurfaced out of the storage space from a rehearsal studio in LA, and was ultimately returned to Modulus which had never been fully paid.
I had a chance to buy the bass when it came back through Modulus. I went up and tried it out, but just couldn't figure out what I'd every do with it, and regrettably passed. Allan Woody ended up buying it, and used it nightly during his bass solo on one tour with The Allman Brothers.
David Fung