I would ask for info over at the Facebook Backdraft Owners Group as its pretty lively with new purchases of RT4s.
https://www.facebook.com/groups/293849465285867
Looking at Motor Vaults "about me" on the website and their FB page they mainly deal in consignments of classic and exotic cars. Their Bio says:
With over 20 years of sales, consignment, brokerage and marketing experience of high-line and exotic. Which they do point to another shop to finish the BDR rollers they sell.
https://motorvault.com/our-partners. The Car Vault appears to be their finisher to drop the motor and trans in.
Even the main BDR shop in Boynton Bch FL uses Speed Fanatics to finish their cars. That said, make sure you have who is responsible for warranty nailed down.
Prestige Motorsport has a good reputation for engines, but they're in NC. Pretty far from you for warranty. There are several local engine shops in the Indy area with good reputations, so if something does go awry you can get it covered parts and labor, and not just parts like when your dealing with a long distance builder.