Could you add the other address lines anyway, even though some are missing? And do you know which is connected where and which are missing? I think A9 was wired to an LED so is inconvenient but I don't know about the others. You could possibly alter the read/write methods to shuffle the address to avoid the missing bus lines.
Also it's not completely impossible for a very determined hacker to solder to an unconnected pin if you take care to mask off the other pins close by (and know how to get yourself out of trouble when it goes wrong 
)
I don't think the NRD clash is such a big problem, the timing can be deduced from NWR and CS.
The upcoming version of the VGA library uses DMA to the SMC data bus to generate the colour modes, with the signal timings controlling the pixel rate.