If I had 15K to drop on an engine, my butt would have flown in, picked it and any associated paperwork up and flown back home. Can buy a 15K dollar motor but won't go get it in person. That even sounds stupid. No way would I make a purchase that big and not put my grubby mitts on it first.
Daddy said it best. "A fool and his money are soon parted"
I'm not sure how much it it would cost to build 600hp but it does seem like 15k could build a really nice engine at a local machine shop. Especially if you did your homework and gathered up the parts yourself.