Modern Vespa

Hey experts! Need some clarity on this from others with more experience...

Anyone know what's the difference in styles between these two drive/output shafts, which I believe are from early-60s largeframes?

One has threads going all the way to the tip, past the cotter pin holes, and it seems less common as I am looking through reference books and parts suppliers etc.

The other shaft, with the threads ending before the tip, I'm pretty sure is for VBB2 (1963/4 onward) models, and possibly others.

The splines that mate with the rear hub look the same on both types. What models and years employ the really-thready one in the first pic?

Basically, I want to figure out... are these two styles interchangeable in a VBB2 engine rebuild?

Are the selector rods also different between the two shafts?

Ok, fun fact: I spotted the extra-thready drive shaft in my Haynes manual, in which he's rebuilding a 1964 Sportique (basically, a VBB made in Britain). All the others I've seen laying around here are not threaded all the way but instead smooth near the end.

I'm currently building a '64 VBB project (I've done a few already...), but I replaced the worn-out drive shaft that originally was in it with this decent used one that's all threaded.

My main concern is that the selector rods would be the same between the two types of drive shafts shown above (if anyone knows!). It was really, really hard getting the selector box slide block...
https://www.scootermercato.com/Scooter-Parts/Selector-Box-Misc-Parts/46613

... to fit into the selector rod, and now that it's in, I hope it works!

The rebuild is all buttoned up. I test-started her on the stand and it ran well. I drained the gear oil because I want to remove the selector box again to double check that the arm and block are aligned correctly with the selector rod on the drive shaft. Usually the selector box attaches easily but not this time and the roller alignment isn't perfect.

Checked it again. The selector rod end in this drive shaft happens to be pretty tight where the selector arm rod fits. But it's back together, the shaft rotates ok and it works fine