A postscript; got the new fuel strainer for the petcock, This had been running perfectly on my little test tank after going through the carbs. Put it all together left it idling while I went to get the helmet for a test ride and gas pouring out the carbs.
Zactly like where I started a week ago.
Used the borescope, tracked the leak to a fuel fitting into the #1 carb. All apart again, All 4 carbs had to come off the aluminum pan, to get that fitting out. O-ring looked meh, my assortment o-ring boxes (fitz-none) didn't have a close match but some square seals from mcmaster carr originally for a failed XS650 throttle shaft replacement fit well. Back together, and out for 20 miles this morning. I'm claiming victory! Great bike, now that it
runs, smooth, quiet, revs happily to 9500 RPM, decent ride for the low seating position, shocks soak up bumps well, compliant. Pretty sure a with little effort it'll wheelie in first. cleaned up nice, still needs some more polishing, clean, lube the chain etc.