Mike,
I took a peek through the web and couldn't find anything the was "specifically" for your '39 1/2 Ton's 16x4 rims.
I did find some sources for inner tube flaps that might fill your need, depending on how wide a surface you want/need to cover on your rims to protect the inner tubes.
None of these are mine, just stuff I found web surfing:
https://www.cokertire.com/accessories/16-rimstrip.html (only 1-1/4" wide protection surface)
https://www.lucasclassictires.com/15-16-Rim-Strip-60.htm (2-1/2" wide protective surface)
https://www.ebay.com/itm/224584729408 (3" wide protective surface - designed for extra wide motorcycle rims with 16" diameter so may also work for you)
Some or all of these may need nips taken out for innertube inflation valve positioning, but should suffice to protect your inner tubes I think.
Hope this info may be helpful.
Dan
