I just took a look at my files and I made 64kb files to burn to 27C512's. Don't remember if I had to or not, I think I just did it to be safe. I use a little program called Hexedit to open the 32kb .bin file, then edit->select all, move to the end of file, edit ->paste and save it. Then you have a 64k file that is 2 copies of the 32k file ready to write to the 27C512. I got all my multi-poker sets from MAME sites and they work fine.
I really like using the Winbond EEPROMs, they have fast access time, program quickly, and you don't have to mess with a UV eraser if you want to reuse one. I can send you the Hexedit program if you PM an address.
I think I remember seeing that on the old board now. I'd be interested in getting a couple of them if you have any extras you're willing to sell.