In order to keep my self-propelled Duraforce 4.5 hp 2-cycle lawnboy walk behinds running, since I have a number of non-self-propelled DuraForce 4.5 hp mowers with very good engines, I was wondering if they were a straight-over bolt-on exchange? Do all the 4.5 hp have the hole in the drive-shaft for the pully bolt?