Scott, I know from experience that Ford Racing sells or used to sell an under drive pulley system for mustangs. I have a set on my 67 fastback. It states in the literature that it is only a track part meaning it doesn't circulate enough coolant at idle for street use. As a matter of fact when my fastback idles too long it tends to slowly begin getting hotter. If I hold the gas at a fast idle it tapers off a bit and then after a while it begins cooling. The convertible does not have this issue as it has a standard pulley system.
I too applaud you for continuing to bring affordable aftermarket parts to the pantera community that actually work and at much less cost than the other vendors.
I would be interested in conducting an actual experiment to see just what happens. I wonder what George has in mind?