Just an update here.
Mower runs perfectly, however, never having used a 4 bladed mower at my place before, and the front yard being a notoriously dry dusty lawn (I always give it a light sprinkle with the hose before mowing), jesus....what a dust storm! Is this normal to have such a huge difference with 4 over 2 blades? I pushed on and finished, but I was sorely tempted to switch off and grab one of the 2 blade victas to finish the job with. Never had that amount of dust with them. If this is normal, I think I might take 2 of the blades off the Mustang, as I cannot see a cut quality difference.