I think you're may be on to something, Jim. However, the 'bolt' (actually more like a long stud) is non-rotational because it's designed to be firmly tightened into the blind threaded hole in the float bowl casting. That means that you wouldn't be able to rotate it to a new position (to take advantage of the eccentricity you're proposing) unless you were prepared to leave the threaded stud-to-casting joint 'loose' after you'd found the bolt orientation position you want. Maybe a thin jamb nut? If that would work (and I'm sure that one or all of Capt Obvious, Blue, Patcon, Grannyknot and maybe even Z Therapy are about to start work on this ), then it would seem that the final touch would be to slot the other end of the 'bolt' (where the lock nut) to allow use of a screwdriver to turn the bolt to make adjustments. Adjusting sequence would be:
loosen lock nut on end of bolt
loosen jamb nut where bolt fits into float casting
turn bolt until desired fuel level is observed inside carb nozzle
tighten jamb nut
tighten lock nut
job done
One additional thought: I don't think the bolt offset needs to be more than 5mm. That would provide an up-down adjustment of +/- 5mm for the float bowl. If you set the float 'tang' adjustment to the FSM-recommended setting to start with, an additional +/- 5mm of adjustment should be more than enough to zero in on the desired fuel height in the carb nozzle.
Gentlemen: Start your lathes. Report back here in a week, with pictures (to prove that it really happened). Whoever wins owes me two finished prototype eccentric bolts.