Stick shift parts! That's a 64-66 bellhousing on the left hand engine. It will let you bolt any Chevy pattern gearbox (or the toploader 3 speed) to a 57-up nailhead. Those don't grow on trees. That and the flywheel could be worth the price the seller is asking for the complete engine.
Also, the 54-55 setup might be useful to someone with an early engine. I would get the whole lot if I lived closer.
Ray