You might find that a ball point pen cartridge or something similar is a push in fit inside the TD venturi.
Even a hunk of lead poured in, piece of wood dowel, etc.
Whatever it takes to get the 128 thread NVA idea going. To make fooling around with these ideas easier to accomplish Harbor Freight sells numbered drill indexes for very low prices.
Hllywdb...I've found that the best sanding tool for the Ranchero's concave "character lines" is a wooly paint roller with self adhesive sandpaper stuck to it. Summit sells rolls fairly cheap of 80, 180, 320 and 400 dry type paper to bring a project all the way through the priming phases and ready for top coat.
I asked them why they don't sell heavier than 80 and they said that a lot of shops prohibit the use of anything heavier because they found more time got spent repairing the deep scratches even though it seems like more progress is made with the heavier grits.
This notion is still controversial with "old Timers" on the discussion boards.
I doubt you would need to "re-jet" the .049 NVA is the .020 is propped for high rpm.
To shave that tiny piston, I would make an aluminum collar with a lengthwise slit that will hold the piston firmly. The "Poor Man's Lathe" idea with a drill motor strapped to a work table on it's side is all you need for power. Use a length of twine or wire to tie off the con rod to keep it from flopping around. Rig up a steady tool rest next to the piston for the back of your Xacto blade.
The shaving process takes very little pressure and I do it dry. Angle to blade so that it is not "attacking" the piston, angle it so that it is scraping the lead-loy piston material. Use a slow speed and make sure that the drill motor is firmly clamped down if you aren't using a lathe.
It's probably good to have a magnifying glass handy to inspect your progress. I've gone almost as thin as an index card on .049 pistons and never had one fail or get distorted.
Every microgram adds up at 30,000 rpm, so figure on how much SPI you can get away with and shorten the skirt before you get started with thinning the skirt.