Tote gote use a 7/8" wide belt, the Minigote belt is a Comet 203789. The original Tote Gote clutch is a Bonham 'Climbaway' clutch. A common replacement for the Climbaway: Comet 20 clutch with a spacer (Comet #200836A spacer so clutch fits a 7/8" wide belt.) The original motor is a Briggs 5hp.
The jackshaft looks complete: pulley, brake drum and sprocket. The bearings and seals are available and easy to replace. The flat bar over the clutch suggests they used an aftermarket clutch such as a Comet.
Sad to hear Billy passed, spent many hours talking with him. He had hoped to get the 3 wheeler running but never had the strength to finish it. Known as 'Mild Bill', he grew up on a Tote Gote. His father 'Wild Bill' operated the Tote Gote shop in Springville, Utah.
The carb shouldn't be hard to find. The 6hp, 7hp and 8hp Briggs engines all used these carbs. The Briggs 'medium flojet' started production in 1938 and ended in the 1990's when flathead production ended. Look for a used motor that has the complete manifold and air cleaner.
Nice build! Can't wait to see it finished. By the way, that head gasket can be found by looking for Briggs Part #270340