Hi H. Sorry, I'm not very familiar with these index gadgets. Trouble is, there are so many possible areas of adjustment, all of which you are no doubt aware. 1. Limit screws. 2. Rotate the body of the front der. on the frame, assuming it's not a braze-on type. 3. Up & down the frame tube adjustment. 4. Fit a barrel adjuster to the front der. Umm, could be tricky, most don't have one, only the rear der. 5. Slacken the front der. cable clamp and put either a little slack or a little tension in the cable, holding it there whilst re-tightening the screw. This might effectively change the distance travelled of the cage when it reaches the index stop. 6. Each model of front der. has only a maximum range of teeth it will shift to and from, hence if you change a sprocket or two, the size may fall outside the specs. Back in the dark ages of ten-speeds and friction shifters, if it wouldn't work properly when correctly set up, then we'd modify the cage with a pair of pliers, reset the adjustments, and it would be fine.
Wish I had a lathe. Saw one today for sale, A$45, had to turn it down. Would you believe it was a treadle-operated job?
Not a toy, either. A heavy flywheel, round groove for an endless rope, the top unit had a grooved wooden roller on a shaft between two plain bearings, with provision to clamp a faceplate, and having a driver prong thing for wood turning. All that was missing was the bench to mount the two pieces on, and the backstop. It must have been durn near 100 years old, and I had to turn it down! Aaaarrrggghhhh!
Clever of you to polish the cones. Truly, every small reduction in friction you make is to your advantage. Did you simply use 400/600 # wet & dry? With kero? Many a time I've wanted to polish ball races. Two identical bikes, but one is smoother in say, the rear hub than the other. The answer has to be in bearing surfaces (finish) and maybe alignment.
Freddie Dixon, of U.K., years back, cut his teeth racing Douglas motorcycles, then switched to cars, Rileys. He was known to be up half the night, stripped the rear axle just to polish the faces of the gears on the crown wheel and pinions. Friction reduction. He'd re-assemble, and invariably win or get a place next day. I saw one of his experiments or inventions once, a disc brake on the front fork of a Duggie, only the disc mounted to the hub was made entirely of that brake pad stuff, and the 'pads' were of steel, I think. Pre-war, most likely. Good luck with your trouble-shooting. And goodnight.