Hello Dirty Harry,
The Shell Valley question is a good one there are two generation of these cars pre Rich Anderson and post. The non IRS Ford straight axel is a good indication, welded steel gas tanks that leak and the frame is box style. The early cars had a custom made coil over shock and a lot of parts that were welded together just for the Shell Valley car.
If you look at the Web site there is still a large list of donor parts that are specified for their build process. I owned one of the early cars and just noticed that it is for sale at specialty sales in Pleasanton. Here is a link to the car and you can see it has a standard hood scoop it is listed as the 1994 blue with White stripes.
http://www.specialty-sales.com/inventory.php
Just looking at it will not give you any clues other than the wheels that were fabricated for Shell Valley at that time...you need to get under the skin and know what you are looking for LOL.
As mentioned earlier each manufacturer has their unique twists and turns to help identify the car. There are cars out there that have never been identified as to their origins......Brent Mills is still trying to figure out where the embyro for his Cobra was hatched.
Best Regards,
Tony R.