No custom grind cams are allowed. Interior has to be as it left the factory and the spare tire and bumper Jack has to be in their correct location. Even the radio has to work. No cylinder head porting is allowed, stock size valve's are required, I don't think that a comp valve job is allowed. Rocker arm's have to be factory stamped steel or cast iron so rocker arms from a 273 are allowed. A maximum of a 0.070" over bore is allowed. Heads can be milled and aftermarket pistons are allowed to help with the increase in the compression ratio which is 1.5 over factory. The actual cost isn't much more than doing a rebuild because of the Strict rules. The biggest cost most likely would be the cylinder heads since stock valve size has to be used would mean having to replace the intake and exhaust valve seats. Carburetor has to be stock but jet sizes can be changed. Ignition system, curve kit is allowed as well as a performance coil as long as it's the same color and size as the factory coil. Any gear ratio is allowed and the converter can't be any smaller than 1" of the stock converter.