Can I make Shimano XTR Shadow 2008 work with road shifters and hydraulic disk brakes I am getting a new bike (Giant Revolt Advanced 3) and because of GRX being completely out of stock I am not able to upgrade the GRX400 that comes with it. I will have to do it later. Since I have a Shimano XTR Shadow 2008 groupset in very good conditions, my idea was to mount this group but only with two chainrings. This way I can sell the GRX400 parts and not lose that much money since I do want to upgrade whenever becomes possible.
Now, my question is if there is any way of having brifters (Sora?) working with XTR 9 speed mechs and at the same time compatible with the existing hydraulic disk brakes (GRX400)?
If I must guess I think this may be an impossible mission but not Tom Cruise style, with some kind of workaround possible.
There is no hydro STI that can do the first idea. It would need to be an old cable pull 10 but hydro, and that doesn't exist.
The first obstacle with your FC-M970 in BB86 idea is even if you jank it together with spacers, the bearing contact areas of the spindle won't be in the right place. Also you'll be taking a component where one of the reasons it's so expensive in the first place is the machine work done to remove material everywhere possible, and then you'll be adding extra leverage to the spindle in a place it wasn't designed to take it. Someone may make a conversion BB that does it better, but then you're eating into the money you're trying to save.
Providing you solved the above, published chainline for FC-M970 is 50 and 46.9 for GRX 2x10 rear ends. So you can make that work if you accept having bad chainline. You are also sacrificing Q and will be spending money on rings that play nice with a road FD, or accepting bad performance of ones that don't.