All that flathead design seems to be 'interesting' It's bad enough working on it in a truck - I imagine a Carrier is somewhat less accessible ....
I had single and twin pulleys break while being posted ( back after being rebuilt ) and I'm less that impressed with the design.
Here's a thought then. Offer the pulley back up to the shaft, and see if it is a sliding fit ( or at least not tight enough to stay on - which I assume it isn't )
If it will slide on, drill a 1/8" hole through the bottom of the pulley groove into the bore, then slide the pulley on and just drill though that hole far enough to put a retainer mark on the pump shaft. Pulley off again, tap hole to suitable thread size, insert socket head grub screw, and then Loctite / grub screw the darned thing to the shaft.
Greetings from Falkirk Nigel - I'll give you a wave tomorrow on the way back to Aberdeen
