Hi Mitch
Haven't got an answer for you, but am 13 weeks post L5/S1 fusion and am hoping to get back to running too. My consultant has said that once the spine is fused, there will be no restrictions on what I can do - including being able to run every day if I wanted
although there's no guarantees I suppose with how the body will cope with it.
Apparently I can try running in about 3 months; so am really really hoping that the fusion will work! Like you I was a fell runner, am desperate to get back to the hills. I've searched on the US Runners World site, there are a few successful post-fusion runners that have posted on the forum there.
Good luck with the surgery and getting back to running.