Pictures, Pictures, Pictures!!! If Brandon has not started on the work make sure ALL the welds are photoed and it would not hurt to have 2 shops put in writing the the Job done is unacceptable and would NEVER pass a Saftey Inspection. In fact contact the Highway patrol and have them inspect it (they have a guy who goes from inspection station to inspection station to certify them), who could look at it and raise H@!! about the inferior job, then take your documents to court, with a time table of events, how long they had it, the conversations you had about your missing parts, ect... You will have a very strong case. Take a Certified Welder with you to court and have him tell the judge just how bad the work is.
I am completly shocked that any one with any shred of Honor or pride would let that type of work ever leave their shop.
You are pretty young to have to deal with guys like that and the difficultys of the Legal system, do you have a Family member who can help you, support you? Don't be afraid of this guy, he may not be in business much longer so get your money back now while you still can.
And allway pay with a Credit Card, they have buyers protection for faulty merchandise. They will go to bat for you and get your money back! (The Merchant doesn't have a choice really, they just suck it right out of his account without asking permission first!)
I admire your level headedness about this whole thing, not coming here and calling him a bunch of names. That doesn't mean you should let him keep your hard earned money though!