Air box evolution...the development of the 72 can be quickly identified by it's style. The early version (a) was without while later models had a host of interesting changes starting with dual plenums at the rear sides of the roll hoop. The raised short snorkel shape followed, to be replaced by the flat anvil. This was later increased in size to allow better engine cooling and ram effect. The "periscope" was used for a short time and proved to be ineffective towards performance. The final large box style (tall anvil) would be used from then on. ld