My customized 48" deck:
#1, I cut enough material off the bottom of the deck to bring the blades to with in 1/4 inch above bottom edge on the front and both sides. This increased the air flow.
#2, I had a friend at a metal fab shop cut a strip of steel, 1/8" thick X 3/4 wide the shape of the deck from one side to the other on a lazor cutter. Weld this flat to the bottom edge of the deck to stop the blow out.
#3, Weld plates over the side vent holes.
#4, To reduce the grass from clogging infront of the collection chute I cut the metal plate back to the edge of the collection chute.
I also altered my steering levers. I cut the tops off and drilled and tapped for a swivel joint in each lever. I used a peice of 1 1/2" dia aluminum rod 4" long drilled and tapped to connect to the swivel joints.I now have a round handle to hang on to and just twist my wrist to turn. Its much more comfortable for my arthurits.