Maybe I've stumbled on to something. I got this:
(5) When a motor vehicle is equipped with other than the original engine or when a motor vehicle has
been constructed, modified, customized or altered in such a way so that the model year cannot be
clearly determined, the vehicle shall be classified for purposes of the emission performance test by the
model year of the chassis.
from this webpage (actually a PDF file) at this link:
http://www.tennessee.gov/sos/rules/1...1200-03-29.pdf
If I'm reading this right, if I put another engine other than what came in the 54 originally, then the chassis (which of course is from 1954) would be the determining factor! I'm off to the junk yard!!