Jose,
FL no longer has an emissions test. When we had an '83 E350/460, I replaced the timing set at around 95,000-miles thinking I'd find it shot. It wasn't but I installed a new set with all-metal sprockets including 0* crank sprocket. At a later time, I installed a FlowMaster "cat-back" exhaust. The part number did not go as early as 1983, probably because 1983 did not have a catalytic converter. A little A-Dapting got it installed, and the extra piece of straight 3" pipe that FM provided for longer wheelbases was all I needed to make up for the length of the cat that wasn't there. It was a 3" mandrel-bent aluminized exhaust that exited behind the passenger rear dual tires. Came out the correct length for the widened body and had a 4" polished stainless tip. All I really needed to get was a 2-1/2"by3" adapter to go from stock crossover to FM's 3" pipe.
I ran an air intake from the radiator support direct to the stock air filter with 4" flexible dryer hose. With those few changes it ran VERY well and power was never an issue. I had tried Headers on a Dodge van we had years before and didn't want to cope with the heat again.
Speaking of Headers, you don't want "Shorty" headers for high HP at RPM. You want Long Tube for low-end torque. Doug Thorley Tri-Y was a popular header for Class C. I believe Thorley may have become part of Summit Racing.
