We ranch and farm, I have had/used Lincolns in the past and have the 18V Milwaukee now. Will never even look at a Lincoln again.
Lincoln's batteries don't last(charge or life) and we constantly kept breaking/cracking the plastic housings. Not near the pressure of the Milwaukee either.
Milwaukee...
To each his own.
In my opinion, pre-heating this particular project is way, way overkill. If he is a good or better welder, he should never have an issue with his welds breaking in the future.
I replaced two shanks on my JD backhoe a few years ago. Also used my Millermatic 252.
Gouge out the original weld with your O/A torch(gouge towards old shank, not bucket), grind out cut if needed and knock off the old shanks.
Clean up your old welds with a grinder, grind the paint off your new...