I have many ideas what the noise could be, ranging from nail in the Tyre to jack rattling around in boot, including loose number plate.
Might help if you provide more info to save some wild guesses.
Dowels aren't really for holding things in place, just aligning.
I would try to machine edges on the girdle and block, and fit correctly sized keys either side of the girdle between the block.
It runs a 14.
That's not fast.
It's impressive , but considering to win a championship like that, turning up to all events and being consistent is all that's required, not a fast car.
So, what's with the title op?
I will answer again in this thread.
The harness would go between the handheld commander and the ecu.
Why not ask the seller?
You don't the commander at all
It will just confuse you.