Thanks for all the contributions so far.
Robin4, this is very good advice... something i've planned to do for a while now (a project in itself) but had not got round to it until recently. I would recommend to anyone the same thing... backup ROM's keeping both a spare soft / hard copy. Motherboards, graphics cards... the lot!
jwt27, I will not use the same ROM... I will probably play it safe and just use a new ROM / flash file. This way if the card boots... it can be used for 20 years+, to reflect and confirm what Robin said.
Moturimi, the kit i'll be using required the ROM to be under the lamp for upto 24 hours. How long do you leave it under for? But yes most of the devices I have that use a ROM works with the 27C256's. If i get some blanks instead of erasing older Bios's (for the meantime) I will be sure to look for and get the Winbond variants.
Thanks again for all the advice so far.