I have made a living on CL buying hybrids and crossing them. Most recently was a 1x8 Felt X:City D, which now rocks drops, a 9 speed cassette and a Suntour friction shifter. Removed the single 42t ring and replaced with a spare, almost identical crankset, but with 44-32-22. Trouble is finding a FD with a weird diameter.
I considered doing what you are wanting to do with a BD 29er. As long as the dropouts are correct, the expense then becomes a new wheelset, but it sounds like you want to keep it SS.