I don't think many cops will look under your car for a stock gas tank or... inertia switches
I'd even ditch the wipers. You will obviously never be able to sell this car as street legal ever again, but you can get away with a lot with show car registration.
5050. The Legislature finds and declares that constructive leisure pursuits by California citizens is most important. This article is intended to encourage responsible participation in the hobby of collecting, preserving, restoring, and maintaining motor vehicles of historic and special interest, which hobby contributes to the enjoyment of the citizen and the preservation of California's automotive memorabilia.
5051. As used in this article, unless the context otherwise requires:
(a) “Collector” is the owner of one or more vehicles described in Section 5004 or of one or more special interest vehicles, as defined in this article, who collects, purchases, acquires, trades, or disposes of the vehicle, or parts thereof, for his or her own use, in order to preserve, restore, and maintain the vehicle for hobby or historical purposes.
(b) “Special interest vehicle” is a vehicle of an age that is unaltered from the manufacturer’s original specifications and, because of its significance, including, but not limited to, an out-of-production vehicle or a model of less than 2,000 sold in California in a model-year, is collected, preserved, restored, or maintained by a hobbyist as a leisure pursuit.
Not sure which if any of these it would go under. I could stop by my friends house and see what he did with his truck if necessary, but I hope AAA or the DMV would know more on this.