In my opinion I don't know why they replaced your 8 year old furnace, especially if you did not authorize its replacement. I would have used a replacement universal motor my self. All I would have to do is know the horsepower-amperage-shaft size and rotation and motor frame type and size and I can pretty much replace any motor in the field today. Lennox has a good reputation and I have never found a motor of theirs that did not have a replacement. All though the contractor may simply have been trying to get you some heat, an eight year old furnace is hardly obsolete. Pulse furnaces are actually a good furnace.