Im sure it will, but not 700 dollars.
True, but you are providing the labor for free. You said you were quoted between $500 - $700 (which seems about the same as a basic HT build around here too).
I think you said you got you bike for $200, +$30 for a front brake? Do you know what your engine kit will cost? I think the going rate for BGFs right now is $180 shipped, so that is $410 right there. So a shop quoting a $500 price is not all that bad, but I can only assume they are basing that off of a $100 bike and no a $200 bike... $700 though, for just a Cranbrook and a generic HT kit, that is a little much. The guys around here that charge $700 at least throw in some paint, springer front end, and some upgraded hardware. Still a tidy profit, though.
But for a personal build, on top of the bike and generic kit, the little stuff adds up too. Upgrade the kit bolts and intake/exhaust studs $10, upgrade the head studs $10, upgrade the air filter $15, upgrade the petcock (supposedly the stock one is junk) $10, upgraded spark plug and wire $10, fuel filter $5, universal oversized front engine mount $15... throw in shipping and you are at $90. So $500 total so far.
Then say you wanted to not mess up those pretty new wheels with a rag joint (and not worry about the hassle), add another $75 for a hub adapter and sprocket.
Then, should the new front brake not work as well as you had hoped to haul the bike down from 35 MPH (I am assuming they installed a side pull brake on the front, for $30), maybe add $75 for a new Sturmey Archer front drum, and another $25 to lace it to your wheel?
Not quite $700, but pretty darn close. And that is without any really fancy stuff like in-frame tanks, snazzy seat, springer fork, etc.
The good news is that it can mostly be done incrementally, but man... it can really add up!
BUT, I cannot wait to see your build. I am certain it will be spectacular!