G'day Chris86,
Before you tear it down any further than as shown in the pics, do a basic compression check. Spin the flywheel backwards, and see if it bounces back off compression.
Parts availability for these small side-valve Briggs engines is generally good, as they didn't change much over ~30 years.
However, it can be pretty annoying to have one that has had minor external parts ratted off it, as some of these parts are priced a bit extortionately.
And you may get a shock if you price a new Honda, good though they are. The current Briggs 'sloper' engines are nearly as good, and a lot cheaper.
Keep in mind that it would be very easy to over-capitalise this machine, given its rarity. Even common wear parts like drive sprockets are not likely to be available.
