True...I do think a real rat would be the following
Take old car.
swap engine with period '50s, early '60s mill.
use period performance parts.
and a little backyard engineering.
and never, ever finish it.
Many current "rat" cars are simply caricatures, no pun intended. An extreme variation on the idea of a "custom" that never made it past a certain phase, was unfinished, if you will.
I suppose the guys with Civics rocking stock wheels with lowered suspension, and with half a bodykit, would be the modern version of the image a "Rat Rod" attempts to portray. Unfinished business.