Amazing what you find when you know where to look...
http://home.thegrid.net/~ffr4776/SB100_Registration.pdf
"So, technically, if your car was built by a manufacturer (for instance, Shelby American, Inc. claims to be a licensed automobile manufacturer (Shelby Series One)) then you can't register it as a Specially Constructed Vehicle; and these cars should meet all of the criteria form the DOT for a brand new car (like SRS/air bags, 5 MPH bumpers, seat belts, anti-lock brakes, anti-intrusion beams, and - most importantly - they should have brand new engines with all the necessary smog and noise abatement equipment on them).
You have to have built your car, or had it built for private use by someone other than a licensed manufacturer or remanufacturer."
This makes it sound as if turn key is ok as long as it's not a licensed automobile manufacturer?
EDIT: The link above was from 2006 (kind of annoying that dates are not obvious on web pages, but a right-click and I was able see that it was created in March, 2006, back when SB100 numbers were hard to get). The author apparently posted this update in 2014--not a lot has changed, other than acknowledging that the SB100 numbers are easier to get and that BAR no longer uses dynos.
http://bauerltd.com/the-magical-sb10...in-california/