PA-28-151 Cherokee Warrior: 1974-76 = 150 hp Lyc. O-320, could run on 80 octane fuel. All Warriors have the 35-foot-span semi-tapered wing. 1974-75 models had large Frise-type hinges on the underside of the ailerons - more expensive to build, but gave better roll response. 1976 model changed to plain piano hinges, same as the rest of the line.
PA-28-161 Cherokee Warrior II: 1977 - on. 160 hp Lyc. O-320, required 100LL. (Many earlier Warriors have since been modified with the 160 hp engine, and there are are a few Warriors with 180 hp conversions, as well.)
PA-28-180 Cherokee Archer: 1974-75. 180 hp Lyc. O-360, 32-foot-span Hershey-bar wing.
PA-28-181 Cherokee Archer II: 1976 - 1990s. 180 hp Lyc. O-360, 35-foot-span semi-tapered wing.
The Warriors have a bench seat in the rear, while the Archers have individual seats in back. Archers have a small hat shelf extending aft from the upper part of the baggage area; Warriors do not.
Warriors have a more blunt metal cowl with large, hinged clamshell doors on both sides (excellent for maintenance and preflight inspection); Archers have a more streamlined fiberglass cowl, with only a small door for oil dipstick access. The entire top half of the cowl has to be lifted off for maintenance.
Archer nosewheels and tires are the same size as on the main gear; Warriors have smaller nosewheels and tires.
Otherwise, aft of the firewall, they're identical.
For 1978, both Warrior II and Archer II changed to the large fiberglass wheel, strut and brake fairings, and the "Cherokee" name was dropped.
1979 Warrior II:
1979 Archer II: