Grumpy, it sounds like you have a direct mount pump. These are either a 9 tooth SAE "A" flange (2 bolt) or a 13 tooth SAE "B" flange, 4 bolt as I recall. If the pump is a small displacement of say no more than 5-8 GPM then it is likely a 9 tooth A flange. There is no key holding the pump shaft to the female PTO shaft, only the pump mounting bolts hold them together. What you are referring to as a key is probably one of the teeth on the pump shaft. I say this because, as you point out there is no way to get at it and since the Allison PTO mounts above C/L and against the frame it is very difficult to get a good look at it. I'd suggest you remove the PTO/pump as a unit and once it is on the bench you should be able to get them apart. Be carefull not to crack the PTO case as these are S-P-E-N-D-Y. You don't even want to know what a replacement Allison PTO costs.
