We have a local man here that used to display at the Glenmoore Concourse show. He would build around 1/5 scale cars with full working engines and transmissions.
He has repo Small block Chevys, Flat Head Fords and even V12 Ferraris engines. Some had working superchargers. He had a few chassis all welded together with full suspensions and some with bodies. It was a real joy watch these things fire up and run. The work and skill that goes into this stuff is amazing to me. Also the tool you need dedicated to this is not cheap either.
Leonard Wood created a 1/2 scale replica of the FE427 side oiler engine that powered the 1967 GT40 MKIV that AJ Foyt and Dan Gurney raced to victory at Le Mans. Hand made out of a solid block of Aluminum complete with working internal parts. Crank, connecting rods, pistons, cam, solid lifters, push rods and working valve train in aluminum cylinder heads. Exact 1/2 scale specifications right down to the intake manifold, valve covers, deuce 4bbl carburetors and Bundle of Snakes exhaust system. Incredible!