I would not weld the gear. The impeller is pot metal and will not hold a weld. It will end up expanding from the heat of welding and when the weld breaks the impeller will spin on the shaft. Been there, got the t-shirt.
What ways have you guys tried welding it Travis ? I have good luck with the ones i have welded so far , but drill 3 holes in the cast around the circle fairly deep , submerge the pump i water while welding to protect the seals , burn it in hot with a tig , and make sure the weld penetrates into the shaft mostly , that way even if the weld doesnt stick to the cast or it cracks the impeller cant spin because the welds act like "keys" and with the pump submerged ( all but were welding) you have no fear of hurting the seals , not guaranteed to work but i havent had one fail yet this way if welded right using stainless rod .
And Jason , Drive pressure wont cause an over heating issue , but would / could explain the pipes .