Stop using that word "RARE"! :beige:
My recommendation is not to use that RAM upgrade board. It looks like the PSU is the intact original first generation as well. It still has the heat sink attached across the top of the analogue board which was designed to increase heat dissipation, however, it had exactly the opposite effect and traps heat inside the unit.
What is rare is that it is still functioning in this condition. It was standard practice to remove that metal strip during the first repair (which thanks to the strip was guaranteed). The first analogue revision promptly removed it.
The RAM upgrade draws a lot of power and all those 256 chips produce an awful lot of heat (far more than 4MB SIMMS in a Plus). And I would expect H3NRY is correct, most of these RAM upgrades required a 512K RAM upgrade to begin with. Which means your stock board has likely been modified. And as he suggests it would have most likely required software to tell the Mac about the extra RAM with the 64K ROMs. But unlike H3NRY, I would not suggest you go looking for 128K ROMs, to fire it up with. Enjoy the stock analogue board (and most likely components) which is pretty rare, and maintain it as a classic example of an upgraded 128K-512K. But definitely use it sparingly, as that fin really needs to be removed and if the components really haven't been replaced, they are just waiting for any excuse to fail. And start looking for an original 128K board to one day replace it with.
After you remove the RAM board, make sure you adjust the voltages which will fluctuate after removing the draw of the expansion board.
While I have never seen this particular RAM upgrade board (and may indeed be a somewhat "rare" one), there is nothing special about them. They were a very popular enhancement back in the day and the cause of many an analogue board failure. Collectors really don't value them, and as you may have noticed, a 128K in pristine stock condition is far more valuable (and enviable). So remove the board, put it in a drawer and get it out to play with on a cheap 512Ke when you eventually buy one. Do your best to keep the 128K strain free and operating with as many original components as possible (which yours looks miraculously blessed with). Check the voltages regularly and at the first sign of odd behavior, start looking to correct the problems. If the caps are mostly original, just start replacing the major culprits until the problems go away.
