The 1st place to start would be the distributor pickup. Check to be sure there is voltage at that switch when the key is on. After that rather then throw parts at it, look for a test procedure.

I'm pretty sure there is a test procedure available on line, I would check for one with a simple search "no spark on 91 Dodge ram"

I've BTDT on a '93 360 Ramcharger. After chasing many dead ends, turned out to be a bad ignition switch. I'd already given up on it, took it in for a 5.7 swap, those guys found the bad switch. FWIW, YMMV, etc. etc.

He has power to the coil, and the motor cranks. the Ignition switch is good.

Could be as simple as a bad coil, or a bad cap & rotor, or even a bad coil wire (parts being new no longer means the parts are good).

The distributor pickup is sounding more and more like a better starting point. I'm not sure what year they moved them from the distributor to the back of the head. Find it and swap it out from your running donor truck.