I just changed to 1×10 last week using my XT785 cranks. The XT bolts are the right length. I had to move the bb spacer to the non drive side. Got a RF n/w 32t and added a Hope 40t t-rex to my XT771 11-36 cassette after removing the 17t cog. Clutch mech already fitted.
I had a day out, after converting, around the Black Mount and found the range was great for me. Managed any climb that I could with the old setup and never dropped the chain once.