I'm sure that it was listed under Grand Wagoneer, not Wagoneer. The XJ Wagoneer would have had the bypass style heater valve. I'm familiar with the differences because I installed a 2 barrel intake from an 83 AMC Concord on a 76 AMC Pacer with a 258 inline six, and between 76 and 83 AMC went to a coolant-heated intake manifold which required a heater valve with a bypass, so that you could shut off the coolant to the heater core in the summer while still allowing it to circulate between the radiator and intake manifold. I think they used the same ones on 4.0 engines as well. The heater valve that they show for the Grand Wagoneer is a non-bypass type, like the ones used in old AMC inline sixes.
Anyway, you all have convinced me. No heater valve! Thanks!