Have you considered an adapter like this:

https://www.ebay.com/itm/Silver-Bott...e/221233824438

I've had good luck with this particular one, since some Schwinn BB shells have a ridge which other adapters can run into - this one is tapered in just the right spot, though you mention the YST, I have no experience with it.

This adapter would allow you to use a standard bottom bracket, perhaps like this:

https://planetcyclery.com/campagnolo...english-thread

The Nervar Stars may take ISO / Square Taper ... and may need a 115mm spindle ... have also seen it as 117mm (might be able to add spacers to a 115mm)

VeloBase.com - Component: Nervar Star (earlier version)

Schwinn Sports Tourer Bottom Bracket

Another option which might work though these are a little long at 118mm (these are somewhat rare, and this is a good price IMHO),

https://www.ebay.com/itm/Schwinn-one...e/223307716110

should allow you to keep existing Schwinn cups and bearings, etc. though the taper is JIS.

I'd probably opt for the first suggestions (though the original BB cups can be a challenge to get out, a little PBlaster and leverage are helpful).

Another thing to be aware of, make sure you have the correct puller for this crank, it's possible it takes a slightly different one, as does the TA Pro 5 Vis ... or it may be standard.