The oil consumption has probably killed the catalyst. The phosphorus in the oil (antiwear additive) is a permanent poison. 1qt/1000 miles is a LOT of oil consumption for that small engine.

You MIGHT try a high speed/high load 'burn-off' attempt on the catalyst before changing it. Also be sure the timing is right on, the EGR valve, plumbing, and passages are clean and working properly.