Go to nhraracer.com then to Stock Car Classification on the left side under the Tech area. Click on Plymouth 1971 open the PDF file and scan down to line 253 and 255. Scan over to the right and read the weights under the engines with the single * . That is for the stock class cars. Note that the 340 Duster weighs 274 pounds more than the 318 Duster. I can't explain that either but I don't know any other way to find the weight online. As an aside, they show a similar Demon at 2884 and the Dart Swinger at 2893.