dodgeman is spot on (again...)

hot rods with repro chassis are classed as an MPV. they have to meet 1949 regulations in regards to light intensity and safety etc - however, there are new national laws brought about as a joint venture between the NHRA and the RTA covering minimum sizes for chassis (100x50x3.0 box section for pre '34, 150x50x3.0 for post 35), max wheel widths (10in on the rear, no more than 4in difference between f & r), max engine sizes (6.0L for pre 27, 7.55L for 27-34, normal engineering regs for anything 35-49).

it's curbed the disturbing trend of "rat rods" - a rusted out 22 T with a big block, 4 wheel drum brakes, 18 x 3 wire front wheels with 15 x 12 rears and rusted out 'speed holes' for the salt flat racer look.