Hi stu45 and grumpy, as far as I know there is no difference in the engine mountings for either the Kirby/Lauson/Tecumseh or the Briggs...though Briggs used a 2.5HP on the 14" and 17" mowers and the 3HP on the 20" mower. The clutch assy on all models is identical. The only chassis difference is that the early Model 45's had a solid engine deck and the later models had the twin rail decking. The engine mounting position was also common to all models.
Re: the Honda G100... it has been replaced in the Honda line-up by a new design and unfortunately probably manufactured somewhere in Asia and not in Japan.
However....some dealers (Honda Power Equipment)may have one or two in stock and these are the more desirable engines.
grumpy prefers the older Briggs engines possibly for originality in the restoration....I chose Honda for
functionality .....one pull starting, the spark plug has never had cause for removal in over 7 years of regular use....it's just a great little performer.
