I am quite keen to chop the head tube (appreciate this could be terminal).
The top section appears to be the same diameter and the clamp is a separate piece.
I like the thinking on the bars, however I think they will inhibit the folding capacity. I won't be folding it loads but handy when I do.
I don’t think I’d start by cutting up the head tube tbh. Maybe some bars a bit like these https://www.tredz.co.uk/.Dedacciai-Crononero-Low-Rider-Tri-Bar_48200.htm?sku=126590&utm_source=google&utm_medium=cpc&utm_campaign=Handlebars&gclid=CjwKCAjw5s6WBhA4EiwACGncZarN_p3Qa0dSf6DL40D4cNiuvUCCCpGmnBniOMf7UqiS2-lGBL9FKxoClPcQAvD_BwE could help?
I’ve done the seat post inside a seat post on a stuck post before, if you can get one the right size it’ll be fine.
Good luck, I want to see how this turns out.