Make sure you read the SCCA Solo II rulebook before attempting some of those
modifications. For example stripping out the interior--even removing sound
deadening from the trunk or putting in a space saver spare if the car didn't
come with one are no-no's. Extra rims can be lighter, but they can't be a
different size or offset. Some esoteric things may be authorized in the repair
manual or in a service bulletin that says "To solve this problem, make this
change" But, if there's nothing like that, it's generally NOT allowed.
Questions should be referred to the Solo Events Board for interpretation before
big bucks are spent.