One easy and low cost solution not as yet mentioned would be to fit a Thompson-Simplex (Thun) type chainset. These mount in a standard size shell and do not make use of shell threads. They are found on a great many department store type bicycles so you could likely harvest one for next to nothing at a junk yard, dump, bike co-op or similar venue. They mount and demount without the need of any special tools.

BMXmuseum.com For Sale / Thun Thompson 2 piece cranks

Vintage Thun Crank Crankset Bike Chrome 36T 125mm 431 | eBay

Here is a set of this type of bottom bracket fittings for cottered cranks: