You realize the 8 bit ISA slot has only 20 address lines (A0-A19). That means a maximum of 1MB of directly accessible memory on an 8 bit ISA board -- less depending what is on the motherboard typically 256K to 1MB.
LIM might be able to have more memory but requires some sort of bank switching scheme and/or controller. A 16 bit ISA board could have as much as 16MB directly addressable memory but those are common boards.
Did you ever make a page on your wiki for this board?
If the RAM is SRAM, I wonder if there is a way to dramatically shorten the DMA dram refresh routine for just the first 16k -- would result in a slight speedup. (just thinking out loud, not actually going to try it)
I wondered this too but is seems it's not possible - the DMA controller needs to visit 128 consecutive rows in 2ms, which the 66kHz refresh clock provides nearly exactly. You could though pull all the RAM logic from the system board, then re-gain DMA channel 0 too I guess.