The aftermarket motor I could get only accommodates those trucks with AC as it has a very deep blower wheel and I have the standard, shallow heater box. It was a P129 or something like that. I tried my wheel on their motor and it was just a bit too deep still because of the offset of the motor and mounting plate. However, I did get the Pepboys replacement motor by VDO (for the 86 K-10) and it was twice as powerful as the one I took out and I am very happy with it.
PS: As a side note, I must say I removed a mouse motel of seat cushion stuffing from the heater box and cleaned it all up. Have to guess part of the performance gain was due to partial blockage. Also, the new motor spun so much faster, it destroyed my aged wheel and I now have one of those on order as well.