"Lawrie said he always had to open up LBSC's cones to get them to feed"
Nick, where did Laurie ever state this?
Derek A G Brown's book is the way to go, published by TEE, as referenced and linked by Simon. My own copy is heavily covered in pencilled notes cross referencing and adding to my own rather large file of my own experiments and construction notes.
A ward of warning – miniature ejectors are rather forgiving. Miniature injectors are a different kettle of fish altogether and require considerable precision and a lot more tooling.
Good luck!
Cheers,
Julian