Ebay Score - Pre-Unit Double Gearbox Adjusters

I've often been told that one of the major weaknesses of the swingarm pre-unit is the primary chain. I think the strength is about 60% of the final drive chain. So to keep the chain in good shape you need to have the gearbox tightened correctly, and to help that even further, you should run gearbox adjusters on each side. What I'm confused about is some models apparently only ran left side adjusters, and some ran both. I can't seem to find a correlation. If anyone out there has any information, I'd love to hear it.

Needless to say I picked up these gearbox plates and a double adjuster for pretty cheap to use on the '55 Tbird. But seeing as my '62 Bonnie only has a left side (the top adjuster shown), I will be cannibalize it for that bike.

Edit:
I asked Paul about it and he says, "The dual adjuster is the later type used on the duplex models, but it is the setup you want to use on any preunit swingarm build because the single adjuster setup just doesn't cut it."