Well, dipper links while being a type of cast steel are notoriously difficult to weld. We've had several in the past come through. Sometimes they're fine other times they just go brittle - they're obviously a high strength steel.

Whenever you got a high strength steel whether wrought alloy or cast, it has a brittle microstructure with a propensity for localised hardening under the heat of the arc, particularly a TIG arc with its small but intense heat affected zone.

Tack the parts back together using a close fitting pin to ensure alignment. Tack some sacricial bars to the ends as run off tabs. This will hold the two pieces in the correct place while you grind. Tack a stiffener across the two ears at the very end to stop it distorting so much.

Double vee preparation to full depth with a root gap of 1/16-3/32" . Ideally a high strength low hydrogen electrode. Either VacPac or baked 7016/7018 would be my choice. Filarc 56S or Conarc 49C.

Preheat the entire part to at least 100-120°C.

Run your first pass on the inside of the ears. Then you can easily grind the backside of root out from the outside and weld over that to ensure no trapped slag or porosity.

Preheat again if necessary.

Weld out as normal ensuring interpass temperature doesn't exceed 200-250°C

Cover in sand or vermiculite in a bucket or tray to slow the cooling time to a few hours.

I think this is a good plan.
I am just worried about your electrode; they are all 7016 or 7018. And according to AWS A5.1, they have a yield strength of 400 MPa/Nmm². I would rather use an 8018, which has a yield strength of 550 Nmm², because you want overmatching.