I would have thought that it should work straightforwardly under 7.6.1; the ppc upgrade cards reportedly required only 7.5.2 (buggy) or above. There was a NuPower extension that went with the card, but I do not recall that it was required for the system to boot. (I have one of these cards, but prefer the 68LC040 in my 540c.)

If it will not boot, I would suspect that the card itself is dead, or that ram needs reseating, etc.