[Myron Piatek]

My interpretation of "original clasification" is the car's "natural" class.
Different versions of the same car, like a regular 1978 Volare compared to a 1978 Super Coupe Volare.....the Super Coupe Volare will weigh more because of the extra spoilers, flares, etc. After doing the shipping weight/engine HP math, the heavier car may "naturally" fall into the next slower class.
i.e.: regular fits "I", Super Coupe fits "J". So the regular Volare can be weight-adjusted to run H, I or J while the Super Coupe can be weight-adjusted to run I, J or K.

To get out of those classes, one would need to change the car to reflect some of the differences within the model lines. But it usually wouldn't be more than one class difference.

I'm also not sure on what the crate engines are suppose to use for the engine in the NHRA classification guides. It once was the largest small block or simply largest engine used in that line of cars as a baseline. In other words, a 360 crate motor combo would use the heaviest 360 shipping weight, not a 318 or 6 cyl. shipping weight. (Unless, for example, a 6 cylinder was the largest engine available in a particular model, like a "Feather" Duster in 1976.) But good luck trying to get it that light!

Using a big block in a car that wasn't available with a big block would still use the heaviest engine combo in a given model line, like a 360.

Double-check with tech to be sure.
Hopefully Duane Eiskant will be back to clarify any questions.