So an Internet injection point for radiograms is https://nts2.arrl.org/radiogram/ but… Remember the US licence conditions and agreements limit which countries are US amateur can sent traffic to third parties. Depending on your destination they may not be able to send it. Beyond that, there is not always an organisation in your destination country to accept or relay that traffic :-(

Well there are some Doug Demaw books on scribd.com which might be of appropriate vintage ( QRP classics or W1FB Design Notebook for example ). Maybe search ‘QRP’ in the books section of archive.org but I’m not so confident on that one.