Here are excerpts from my mail that may help anyone wanting to build a single-handed recorder. These are bound to stimulate your thinking. Thank you contributors.
From JSW
John Edfores has a book on making PVC instruments that has an excellent chapter on adding keys to plastic instruments. It's a "must read" probably the only book of its kind. There's also a good article in "the Woodwind Quarterly" about how to cut seats for keys and how to make the keys themselves. Second, I've been tinkering around with single handed keywork on Yamaha recorders for years. Your idea about cutting the recorder in half and reassembeling it is rather different from my usual procedure. What I usually do is to fill in whatever holes holes that should be "moved" and cut other holes. This way, my new holes can have flat seats and raised edges (look at the holes under the keys of the Yamaha tenor or bass, for an example) making the keywork altogether easier. This also is useful for having more than one thumb hole opening (a small one where you would crack or pinch, and a larger one for notes where it's normally full open). It's also easier to experiment with keywork for the double holes when you can separate them.
p.s. another thing about filling in holes and drilling new ones.... You can drill more holes than you fill in, and use the keywork to eliminate a weak cross fingering or two, if you want to "modernize" a recorder at the same time. I've always thought the double thumbhole (even on a two handed recorder) was a good way to get around that "rolling, pinching" thing.
I got some information from The Flute and Flute Playing (Theobald Boehm translation from Dover). It is nice reading and interesting.
BH