1. I too, tried to contact bygdawg. I decided not to wait, and contacted Red Dirt Cowboy. Yes you need longer bolts. RDC hooked me up, for less than the link to ebay that you shared.
NO trial and error, just one-and-done.
2. Trial and error? With tubular steel? And does anyone besides me think there's a really good chance of weakening the steel bars that you are then expecting to hold up in a tipover or a crash?
Your link to the ebay site shows $170 for the bars alone.
But I got adapter plates, shipped to me, for about $60 and then bought the take-off GoldWing bag protectors from a trike company. The bars were about $35 or so.
The adapter plates - INCLUDING the proper-length bolts - came from
@red dirt cowboy from his link in the For Sale > Vendors forum. Here's the link:
https://www.st-owners.com/forums/th...0-adapter-plates-and-hardware-53-ship.158379/
I didn't use any trial and error - only the instructions that RDC includes with his adapter plates.
And no fussing with a slipping / misadjusted subframe, either.
The way I see it, this is MUCH simpler!
I hope this helps.