>Hey now, there are only needles on the input and lay-shafts, nowhere
>near the mainshaft...
Sorry dude but, the input shaft runs on rollers that engage the main shaft.
The input shaft runs between the pilot bush and the large ball bearing at the end of the bellhousing. The mainshaft is supported by the input shaft vie those magic rollers. The rollers take the full force of the load that the laygear imparts on the front of the mainshaft through all but first and fourth gears.
Using fewer rollers inside a retainer will put more load on individual rollers. I am not sure, but I also think that it will leave discontinuities in the rollers abilities to hold the mainshaft in close continuous contact with the laygears. This due to gaps between the fewer rollers in the same space as the packed rollers.
I have a OD mainshaft at home that ate its input shaft roller bearings.
Not so pretty.
The input shaft is the fastest spining entity in the gear box, and the rotational rate of those little rollers is more than 100,000 RPM at speed.
Something to think about.
Jarrid