I may be of small assistance, maybe.
Just because some of the parts are not metric, that doesn't mean it's an "American" bike. It could
Many bike parts have industry standards that not metric.
One piece "Ashtabula" cranks (like on your bike) have been the industry standard for inexpensive bikes (cruisers) for many decades. Ashtabula is a city and county in Ohio and The Ashtabula Bow Socket Company started making cranks (and other parts) for Schwinn atc in the 1930s. The standard has stuck, worldwide. Your crank accepts pedals with 1/2 inch threading.
The international industry standard for ALL other cranks is a 9/16 inch pedal hole.
The international industry standards for fork steerer tubes are 1 inch, 1 1/8 inch, and now 1 1/2 inch.
Shimano (Japanese company) makes inexpensive front hubs and coaster brake rear hubs, common to cruisers, that use 3/8 inch axles.
International industry standards for bearing balls are also measured by fractions of inches.
Some handlebar and stem dimensions are referred to and sold by their non metric measurements. Some not.
Bottom line, ALL bikes, old and modern, from France, China, Italy, America, Germany, Taiwan, etc, have many metric and non metric parts blended together.
If that isn't lame enough, let's not get started on the insanity that is the lack of uniformity on bicycle wheel and tire measurements.
That said, here is my effort to help. I have no clue who made that bike. If you don't get an answer here, try this website/furum. It is specifically for cruisers and rat rod bikes, and these guys really know their stuff. They are very friendly and very helpful.
Good luck and thank you for your service.
Rat Rod Bikes - A Community of Custom Vintage Bicycle Builders