Question about Flowtech Shorties

[W_O_T]

I just bought a 90 c1500 with a TBI 350. I'm looking at ordering some Flowtech shorty smog headers, but they have 2 different part #s for my application. One is compatible with the A.I.R. injection pump and one is not. Being a Mustang guy, I've never owned a Chevy before this and have no clue what the A.I.R. system is. Is this some type of emmisions equipment or what? Also was it even available on 1990s? The part #s cover from 88 to 95.

[99Silver6.0]

Flowtechs are really lacking in the quality department. Seen alot of them blow primaries loose from the flanges. Quite a few! Check out some Edelbrock or JBA's if you want shorties. Being a 90 Silverado Id almost bet your truck has a smog pump on it. Least my old 88 did. But I took that broken ass thing off.