I think that there is some confusion here.
The early Mac models have ROMs that are in a DIP package. Examples: 128K/512K, 512Ke/Plus, SE and SE FD/HD. Later Macs (SE/30 and IIfx) had ROMs on SIMM, whilst others (IIci) had ROMs soldered to the board with an unused ROM SIMM socket. The IIsi was available with soldered ROM and, more rarely, with ROM SIMM. IIcx ROM type, anyone?
From this photo, it looks like the Mac II uses DIPs (sorry, I don't have the motivation to crawl around my collection tonight):
http://upload.wikimedia.org/wikipedia/commons/8/8e/Macintosh_II_motherboard.jpg
Note the four socketed DIPs next to the SIMM sockets. We can assume that the IIx layout is similar, because the ROMs were sold as an official upgrade to Mac II owners. The upgrade was useful because it allowed the use of the FDHD floppy AND improved RAM SIMM compatibility in Bank A (you still need PAL SIMMs and a 68851 PMMU or 68030 accelerator).
Repackaging the SIMM ROM types in DIPs is no doubt achievable but you need a lot of motivation to try it. Trag knows about repackaging soldered ROMs as SIMMs from his work on the IIci SIMM for an SE/30.
The early Mac models have ROMs that are in a DIP package. Examples: 128K/512K, 512Ke/Plus, SE and SE FD/HD. Later Macs (SE/30 and IIfx) had ROMs on SIMM, whilst others (IIci) had ROMs soldered to the board with an unused ROM SIMM socket. The IIsi was available with soldered ROM and, more rarely, with ROM SIMM. IIcx ROM type, anyone?
From this photo, it looks like the Mac II uses DIPs (sorry, I don't have the motivation to crawl around my collection tonight):
http://upload.wikimedia.org/wikipedia/commons/8/8e/Macintosh_II_motherboard.jpg
Note the four socketed DIPs next to the SIMM sockets. We can assume that the IIx layout is similar, because the ROMs were sold as an official upgrade to Mac II owners. The upgrade was useful because it allowed the use of the FDHD floppy AND improved RAM SIMM compatibility in Bank A (you still need PAL SIMMs and a 68851 PMMU or 68030 accelerator).
Repackaging the SIMM ROM types in DIPs is no doubt achievable but you need a lot of motivation to try it. Trag knows about repackaging soldered ROMs as SIMMs from his work on the IIci SIMM for an SE/30.