1) Some A3000 have KS1.4 Boot-Roms which load KS2.04 or KS1.3 from hard drive into RAM. Make sure you dont have BootROMS. If you do... you could change the files on your hard drive so that it boots to KS3.1!
2) There is no MAPROM jumper on the regular A3000 (If you have an accelerator there may be a jumper on that). If you dont have BootROMS, the loading of the ROMS into fastram must be part of your startup-sequence on your hard drive.
Check your startup sequence on your hard drive and look for anything that might be it. (Print it here and we'll tell you).
3) You have to remove and replace the ROMS that are fitted.
There are several types of A3000 motherboard, several different pinouts of A3000 kickstart ROMS. Get the wrong ones and it wont work (without a device called a ROM tower)
4) Remember they have to be A3000 ROMS for the SCSI to work.