Hello Lynn,
Thank you for your detailed reply and for your extensive research. I greatly appreciate it.
Here is an internet photo of a same model REO Speed Wagon truck as mine accessed 28th March 2022 from,
https://www.smartcycleguide.com/L49132542. The photo has the truck parked in a wooden barn.
Of course the photographed REO truck is in better condition than mine. Unlike the REO truck in the photo my truck sat in a paddock for 40 plus years after it was parked up by the previous owner's father. Since I have owned my truck it has been sitting patiently in my shed. By then the weather had not done my truck any favours though. The next photo is my REO parked beside its stable-mate, that is also waiting patiently in my shed for some attention. However, things like the white one keep usurping their place in the queue.
Notice that the wooden barn REO does not have a radiator cap either! Must be a common occurrence - leave a truck sitting for a while and someone nicks the radiator cap.
Kind regards
Lionel