The T4 engine was to be used in quite a few other vehicles as well, including the Porsche 914, and the Porsche 912E models, as well as being used in the Bay’s successor, the T25, and being the basis for the waterboxer as featured in Type 25s.
Along with the aforementioned engine changes the Bay window also underwent several cosmetic changes throughout its lifetime. As early as February 1968 VW had already started making changes on the Bay, the hazard warning light switch had changed, there was a firewall put in place between the fuel tank and the engine.
In 1969 more changes were to take place, the cab doors were now lockable from inside via a small catch above the door release as opposed to the pins of the previous model. The external door handles were changed from a push-button type to a trigger type. There was also a small number of electrical and detail changes.