Burt, if you have a few days to spare I'd recommend going to SDP-SI for timing pulleys (
www.sdp-si.com). Their selection of GT2 & HTD pulleys beats the pants off McMaster, and they're quite a bit cheaper. We've been using their polycarb w/ aluminum insert pulleys on our shooter for the past month with zero problems.
And as an FYI, most curved-profile belts and pulleys are compatible, so an HTD, GT, or GT2 pulley with work with the 5mm pitch belt provided in the KOP.