CA Capillary Conversion Part Referrals?

All looks good.
I got my reducers from Heatcraft, part number 1009-0804. Not sure if that part number is known in the U.S.
This is typical of what you need www.ebay.com/itm/Elkhart-Products-118-1-2-1-4-1-2-X-1-4-Copper-Fitting-Reducers/282432651342
When working on the unit charged, keep the charge valve slightly open as the pressure may start to build up otherwise, because of rise in ambient temperature, or picking up heat from the blow torch. It's best for it to release at the charge valve and not at the pipe you're soldering.

Thanks for all the advice so far! All the required parts are on order, I found Dad's manifold gauge set, and we're mostly good to go.

Next question: which of the bewieldering assortment of methyl formate should I order from Sigma-Aldrich?

www.sigmaaldrich.com/catalog/search?term=Methyl+formate&interface=All&N=0&mode=match%20partialmax&lang=en®ion=US&focus=product

Thanks!

I will be curious to know how you go getting the methyl formate, given the restrictive sales policy of Sigma Aldrich. Some here have been successful getting it, but others haven't.
If you are going to leave the existing methyl formate in the system, you shouldn't need to add any. Provided you make up the filter, reducer & cap tube as a sub assembly first, the system won't have to be open for very long - certainly not long enough to worry about evaporation in a cool location. I have always found the capillary tube conversion favours a slightly lesser charge anyway.

I did quite a few disconnections/reconnections of cap tubes on the kitchen floor when I was doing the experiments to find the optimum size, and length of cap tube for 50 cycle operation. And yes, the methyl formate vapour was sometimes enough to ignite, despite the presence of nitrogen - it burns with a green/yellow flame. The intensity was like that of a candle, and was easily blown out. Having said that, I wouldn't be complacent about it. Blow it out soon as it ignites.
I know it's stating the obvious, but make sure your blowtorch is actually capable of melting silver solder on half inch tubing - some say they are, but are useless for anything over 1/4" tube. You don't want to be stuck with an open system you can't seal up quickly. I was fed up with the modern MAPP gas replacement, so have since used an oxy/propane torch. Another thing too is the cabinet top insulation is flammable, but this shouldn't be a problem for where you'll be soldering. The grommet around the float valve will melt/burn slightly but that's difficult to avoid. I've used a wet rag around the area or a cooling gel which work well enough to stop it being totally destroyed.

Blowtorch on kitchen floor 😬
I wouldn’t have to worry about the refrigerator my wife would string me up ! 

acid flux + POE+410A causes problems. Carrier knew it when they first introduced Puron (410A) in 1996 and told us to braze the 410A systems. I always braze and flow nitrogen on 410A systems as.