[1] There are 'poly' gears for some engines, not sure if for Chrys. A company called BOP Engineering makes some. They work with any cam.
[2] Where are the instructions that say you cannot use the Melonized gear with a cam that used the bronze gear.
[3] The collar on the dist shaft is NOT there to stop upward thrust. Do you think a thin plastic collar would be used if that was the case. The thrust is DOWN, caused by the oil pump loading the gear. That is why the bushing in the block has a shoulder on it, to take the thrust.
There is no locking collar from the factory, and the gear can ride up and down during acceleration and deceleration of the valve train. Yes, the vast majority of the downward contact the intermediate shaft has is on the bushing in the block. The gear pattern pushes it down into that bushing by design.
The tang at the bottom of the distributor drive shaft, by design, typically does not bottom out in the slot on the intermediary slot. If it did, it would cause wear to the distributor and the plastic collar you mentioned, but since it doesn't, there's quite a bit of room for upward travel of the intermediate shaft. Which does happen during the dynamic action of this style of gear set, the thrust motion of the camshaft in the motor and the thrust action of the intermediate shaft on its bushing. I believe this is refereed to as backlash or something else. This dynamic movement of the gear set components is why roller cams control in AND out directional changes during running with both a thrust surface and a cam button. Cams should just be thrust backwards because of the thrust angle on the cam gear, but thy can move both ways when the engine is accelerating and de-accelerating.
This results in changes to the contact pattern on the gear sets. That should be and can be best controlled, especially with roller cams, for multiple reasons including lifter/lobe ride patterns, but also controlling the position of the cam gear. That's why the backlash on rearend gear sets is set-up so carefully to avoid excessive play for either gear. The ideal scenario is where both the camshaft's fore and aft movement AND the intermediate shafts up and down movement is carefully controlled being sure to allow enough freeplay for an adequate oil film especially on the intermediate shaft to bushing surface. With the manifold and valley pan removed, I use a feeler gauge under the intermediate shaft gear, install the locking collar on the distributor shaft just snuggly and then bolt down the distributor. This sets the clearance and results in a much more stable position of the intermediate shaft gear in relation to the cam gear.
As evidence, look at the wear on a bronze gear where there is no collar on the distributor shaft, versus the wear pattern on a bronze gear that has it's upward travel limited by collar affixed to the shaft.
It's significant, and not controlling this freeplay greatly increases wear on the softer bronze gear. Observing the odd wear pattern on my first bronze gear is how I figured this out. It was before cell phones though, so I didn't take pictures.
