All he has to do is check the bios rom to make sure the clocks are in the limits of the 8800gt and the only thing that can complicate things is the timings on the vram but that usually doesn't pose to much of a problem. I can even mod the bios of a 9800gt to where it can be used in sli with either a 9800gtx or a gts250 by changing a few things without even touching the clocks, timings, or even what is enabled or disabled. The advantage to all these cards is that the core is all the same on all models except for what is enabled or disabled. The rest is all dictated by the driver and that is a different topic altogether.
Fermi era cards are different and pre geforce 8 era things can be changed but there are limitations. Fermi cards are more locked down and restricted than what people in my day enjoyed.