Never really worked, and I did it as an experiment more than anything else. All from salvaged stuff so it didn’t cost anything, but I suppose I could move the pivot down and set up a similar system to what everyone seems to go with here. With the brakes I used, I never had enough leverage and riding on mud resulted in a massive buildup which would stop the wheel from turning.
Did it! 107mm brake arms just clear the 3" tire (I bent the metal cable housing elbow that connects to the brake a bit to get a couple more mm’s clearance). I did pop for the Tensile adapters (https://www.tensile.net/tensile-magura-vee-brake-converters.html), which put the v-brake mounts about 10mm below the bottom magura boss on the frame. I would get that 10mm back with homemade adapters that attached at the bosses.
It looks like your brake is not giving you enough travel. Your straddle cable is pulling almost straight up, and so it isn’t putting as much energy into moving the brake pads towards the rim. To fix it you would need calipers with longer lever arms so that they could clear the tire, and have enough spread to give you about a 45 degree angle on the straddle cable. It is possible that you could make your current brake work with a shorter straddle cable, but I still think you may run into problems with the geometry.
Mounting your studs lower will allow use of a V-brake which eliminates the whole straddle cable geometry problem (the single biggest reason people complain about setting up cantilever brakes).