You can mix speeds so long as the replacement chips can handle at least the desired speed. So 60ns should work fine as replacement for 80ns if all other specs are the same.

Looking at ebay those cards sell for (last couple months) $50 half populated ~$90 fully populated. Can you even buy those chips at less than $1 a pop? Looks like M511000 sell at $2-3 each. Might make more sense to buy fully populated board 😒

This is the only board I could find that would do more than 2MB memory

2 days ago this info was sent in, today I made a page of it:
https://theretroweb.com/expansioncards/s/everex-ev-178-1

I hope this will help you out.

Thank you very much for including this. I had found the software but no documentation or anything else.

I might have found some 1mx1 drams for this board. I have to wait for payday and the I want order 40 of them. then it is figuring out the software for this board. My 286 only has 640k of ram, so have to figure out how to configure this board with this system.

Ok ordered 40 MSM511000C-70ZS from american semiconductor, let's see if they send them. They were not expensive 40 were $36.

Ok got the chips, wrong packages, they said pdip18 but we're single inline packages. Oh well I will keep trying. I did get the board working in my 286 system. Now waiting on my picomem.

I have one fitted with the full 8MB....

Have you got the installation software? I can post it here if needed.

Yeah it is on the retroweb site. I want to outfit mine like yours.