So many restarts - but think I’m finally on the right track. US 4 seems a better size for this yarn - though my gauge is 24 sts for 4”. Wonder if I should bump down to a 3 before I get much further.
Using doubled up laceweight black as substitute for fingering. The stuff was turning my hands blue as I was knitting so it also got subjected to an intense rinse with soap and a lot of water… some spots are almost red now (the water was quite blue - ah, dyeing, you are so persnickety… but at least this one was NOT my fault - I wonder if Cherry Tree Hill is still in business…) The hank was slightly felted in the agitation and rinsing - but was still pretty much separable - so I’m going to use it anyway. Live and learn. Do not agitate MEANS do not agitate.
Catching floats of the darker contrast color wasn’t working - they showed through to the right side. One of the other testknitters suggested an alternate method found here:
https://www.ravelry.com/patterns/library/practice-invisib...
It doesn’t seem to be entirely necessary to catch them at all for this project, as the dangly bits will be enclosed on the inside of the tube of knitting.
Last Note - It was Extremely helpful to place stitch markers at the beginning of each “feather” in the sequence. Some of the testers shifted the markers each row, but I only shifted them at the start of each left/right paired sequence (12 rows, give or take). One of the most challenging, yet satisfying projects I’ve worked on in a long time. This is truly a one of a kind cowl - and one that will mean a lot to me in years to come!
(If only I could guarantee anyone after me will enjoy it after my passing, sigh… but I plan on living a few more decades, at least!) 
03-30-2021
Yardage estimated for contrast yarn: 20 yds of the lace weight doubled is 9 grams. Total weight of the cowl is 192 grams, of which approximately 95 grams is the hand spun. 100 grams of the doubled lace weight would be about 222 yds.
There were 13 yards of the original 380 yards of hand spun.