There are several different drier designs depending on A0 vs. A1 trucks. It is generally recommended to replace the entire drier with a newer design on the A0 trucks as much better is available now. On my A1R truck I was able to order the drier cartridge from NAPA for like $65 or so.
The air system is everything on these trucks. Without air you don't move, you don't stop, even the radiator fan doesn't work. And the system is pretty complex being somewhat combat redundant, etc. You should invest in 1/4", 3/8", and 1/2" air tubing and an assortment of fittings. Older trucks used compression fittings and newer truck use push-lok fittings
Rick