Correct re: remote reservoir shocks being disallowed for pre'75, however your theory of no piggybacks would mean 1974 Yamaha Thermflow shocks (standard fitment to some models) would also be disallowed, which is incorrect. Most modern, replacement shocks (piggyback or otherwise) are built with some sort of external adjuster, you'd be hard pressed to find a scrutineer who would exclude them from competition.
K