Just last year picked up a 7800 sat outside for six years, I put a new battery in and did as above and checked and added all fluids and it fired up right away and died. needed to drain water out of the fuel line and when diesel was running I put it back and started it and drove it home from the...
My case 1840 skidsteer has 12x16.5 tires where 10x16.5 tires should be hard to change since they are near new. BUT the 12x16.5 tires makes grading harder because the bucket is not flat on the ground like they would be with the smaller tires, something to think about.
I am no pro hobbiest. Will need some on the side practice and will want to purge the tube with argon while welding the outside or it will be a mess on the inside. YouTube is your friend
The first step for me would to check battery connections and starter connections and load test battery. maybe first try to jump start with a good source battery.