What kind of EPROM is he using? A 256KB will have too many pins to fit in the socket, surely?
If you want to make it 256KB just repeat the 32KB by appending the file to itself 7 times (or 3 times if you add the resulting file to itself rather than the original file- 8 is 2 ^ 3 after all)
My advice, though: make life a lot easier on yourself and use a 32KB EPROM instead. You won't have to worry about pins sticking out and rewiring address lines and stuff with a 32KB one.
