[Frank Lee]

I have spent an inordinate amount of time obsessing over such a project. Other considerations besides the overall strength and ability of the swingarm to resist lateral (and torsional loads, depending on design) are being able to use the same or similar automotive wheel and tire as the front has, and being able to use an automotive brake (including parking brake), being able to fit a stout enough spring and shock, and being able to change the rear tire without having to jack the rear end up three feet in the air or put some sort of access panel in.

Also... what Yamaha things are you referring to? A quick Google shows mostly single front wheel trikes...