In the past I used one of the softkick tools to load a 3.1 ROM (I had 3.0 ROMs at the time) and run OS3.9. The only one I got to work used 500k or so chipram to load the ROM, I never figured out how to load it into fastram (cheap Typhoon '030 accelerator.)
I'd definitely recommend spending the $20-$30 on a set of 3.1 ROMs.
