A crate motor is simply that, a motor in a crate, fully assembled and ready to go. If you buy one from a remanufacturing company like ATK guess what? It's a rebuild. If you buy one from an OEM manufacturer like Ford, Mopar or GM it will be brand new.
Many of our LBCs' original motors haven't been manufactured in many years. Any of these motors will obviously be used and/or rebuilt unless you find a NOS unit hiding in someone's attic.
Here's an idea for somebody, make a bolt in conversion kit. There are obviously a lot of people interested in it. If you do it for a car that is pretty popular and available like the B or Spit there will probably be enough customers out there to make financially viable.
Choose a vehicle/engine combination that doesn't require any cutting on the car and can be implemented with as many stock parts as practical. The rest should be a fairly small number of simple custom fabricated components, brackets and harnesses.
Sell it as a complete kit, crate motor included, and you should be able to make a reasonable profit with a very modest capital outlay.
PC.