KYB's Excel-G is a dual tube shock. The Gas-A-Just is a monotube shock... higher performance (no foaming) and price; I've heard mixed reviews on which lasts longer. The monomax is an upgraded gas-a-just... Not as familiar with them as I haven't had anything warranting such that needed new shocks/struts.
It's a bit corny with wooden acting, but here's a breakdown from KYB on what's what, in the context of SUVs:
1984 F150: 300 L6, AOD, RWD. EEC IV / TFI, Feedback Carter YFA Carb. Stock everything but radio (for now).