Hi, about your 630 chain tensioner... I have H-Ds so I know!!!
If you run it dry, it will jettison in next to no time.
The shape is fine but H-D runs it in an oil bath hence the nylon shoe will last, but not forever!!!.
Before H-D went really really cheap, they went really cheap then they were just goin' cheap around late 60s.
Before that, they ran a tensioner where a stellite treated steel blade was welded on to the bracket:
You should find in your stash a piece of hardened or alloy steel good enough to allow chain tension durability.
I tend to use old spanners for such hard work, they are cheap and they are indeed special alloy...
On the subject of shifting 2 gearboxes together, I seem to remember Ack Attack had loads of problems a few years back when both Yabusa engines, due to vibration or whatever, refused to shift 5th and 6th gears. 1st to 4th was OK... In the end, they just lowered drastically the final transmission ratio to get the record in 4th gear. Might be worth enquiring to see if they resolved and how that issue recently?
Best of luck from Patrick