Pulse furnaces with a varriable speed blower had a V in the model number.
The 2 models that had them are the G21V upflow and the GSR21V horizontal/downflow units.
The first few years of them had the ICM1 motor. In the very unlikely event one still has an ICM1 motor, there is a kit available from Lennox to upgrade to the ECM2 motor.
I forgot the date, but the units started coming with the ECM2 motor shortly after it became available.