A few years before my time, but didn't we have 3 against Shrewsbury in the 1982 FA Cup Quarter Final? Wallington, Young and Lynex I think. After the regular keeper, Wallington, was hurt and Young went between the sticks, I seem to recall hearing that Young went off injured, Lynex replaced him in goal, but as you only had 1 sub at the time, Young came back on and replaced Lynex in goal again.
No doubt there are plenty of people on here who can correct me. I'd have been about 3 at the time!
That's still only 3 keepers though.