You need a 27C512 EPROM.
I really recommend that you DON'T reprogram your original BIOS EPROM (you would need access to an EPROM eraser to do that). A new 27C512 EPROM only costs about $5 anyway. Best keep your original BIOS just in case.
What version is your current GD SF7 BIOS?
Contact me if you want me to program the 7.11 BIOS into a new EPROM and send it to you; total cost incl. postage would be US$9.