here's a bit of an update for any other brake sufferers.
i put the arm rotation back to 'normal' tho kept the homemade longer arm. and replaced the cam for one that held the shoes better.
i put the older fixed shoes back in (i don't know their history but still lots of meat), chalked them up and found little other than the bits of the trailing shoe were making good contact.
so i made an adjustable rod between the arm and the cable lug, set the shoes open the correct amount (smidgen under 8") and arced the linings in the lathe using a back axle and other bits to mount it. most came off the trailing shoe around its middle. I sanded a bit more off the cam side of the trailing shoe (which makes first contact).
and... its a lot better. not great, but it actually feels like a brake that I can rely on. still abs but i might even need to check the fork oil.
so. lessons for me - start with the basics before getting creative.
there's a low spot in the drum so i might work on that some day and maybe redo the chalk for a retest. but i've had enough brakes for a while.
and here's question - how to hold floating shoes in place so i can arc them on a lathe... any ideas?
make a dummy backing plate.
The important thing is how far is the pivoting ends of your shoes off the drum ?
Shimming the shoes or making up a bigger pivot will make a massive difference.
Every one worries about how close the front of the shoe is and forgets about the back.
If it is measured in 10ths of inches it is too big.
Fitting longer levers is a waste of time.
You can not stop your bike using nothing more than your own grip strength applied over 4" to 6" of travel between you brake lever & handle bars.
You need a rapid pull to jamb the leading edge into the shoe to force the shoe into the drum using the kinetic energy of the drum, not the energy in your fingers.
Hydraulic brakes work differently because you can have up to 4000 psi at the slave cyinder.
Your hand would need a lever with 9' ( yes foot ) of travel to apply the same force.
To get the brakes to work you need the shoe really close to the drum AT BOTH ENDS.
Concentrate your efforts there & you will be rewarded with an excellent brake.
Frig around with longer levers and all you will do is pull off nipples and wear out pivot holes.