Polaroid & lens hacking is a great pastime, not least of which because of the instant results. There are a tonne of web-based tutorials on options, including here in the Articles section. Moomin has some great stuff too. We've done Pathfinders, J33, J66, Fujipets, and all sorts of pack-film, peel-apart and Instax work.
Optically, the roll-film to pack-film conversion is great on a 110/120, but the most fun is possibly the 600SE to integral film. Though Instax on Fujipet was interesting... Good luck!