I do have a stock 128k logic board myself with the original 64k ROMs, but I prefer to use a 512k logic board instead, since it too has the 64k ROMs plus enough RAM to be quite usable. I simply would like to have the best of both worlds. If there existed a driver for the 64k ROMs, then I perhaps I could track down a SCSI SSD which would eliminate the need for an internal fan and perhaps would be low power enough to not even warrant a secondary PSU.
If a 64k ROM compatible SCSI driver really is impractical to create, then it would be nice to have the means to switch between the 128k and 64k ROMs (via mechanical flip switch on the back). Yes, I know I could accomplish the same tasks I desire simply by having a Mac Plus sitting next to my Mac 512k, and I could just use the Plus when I needed SCSI access. But having a single machine that could do both would be better. It would take up less desk space. But most of all it simply would be impressive a single machine that could do that. It would still be "original" in a major way, plus it would have features that only a 512ke, Plus or higher have -- SCSI access.
As to that 3 months of hard coding work, I wouldn't necessarily rule that out. For truly, if I had experience with 68k assembler programming and if I were retired, I can tell you for a fact that would be on my list of fun projects to tackle. Not sure if I am alone in thinking that way, but I do know there are some on this list far older than myself who might be willing to give it a try, perhaps some day. Some may consider such a "waste of time." But then again, some people may consider our posting on a vintage computing site to also be a waste of time. Let's face it, we're sort of geeky. And this is one of those geeky, but not completely impossible, projects to dream about. It keeps the vintage computing enthusiasm alive and kicking.