Filters had been an option with Chevrolet since as far back as 1927. Most of them you see were dealer installed or sold as an over the counter accessory in the dealer ships or auto parts stores. The factory installed option was painted black as were the other bolt on components in the engine compartment and the accessories would have been yellow and black or blue and orange depending on the year. Many aftermarket bolt on filters were sold back in the day, The orance Fram filters being the next most popular to GM's AC filter.
The engine that your have in your truck is a late model 235 and the filter is not a GM AC or a Fram, it could have been from Western Auto or Warshaski's or any one of hundreds of suppliers.
Denny Graham
