351W trucks were SD until the OBDII switch in '96. Trust me, been bumping walls on this one researching my hauler.
I have a K&N, Timing is bumped to 12 degrees, Hedman shorty hedders, and a custom Flowmaster exhaust with a Delta-Flow 40 series 'flow. Not sure on power gain, but I've picked up 2 MPG mostly from the K&N and exhaust of course.
I'm planning to go electric fan, GT-40's off my Cobra, my old Cobra cam, the Eddy intake/TB, and finish the exhaust. I may either do a B10O MAF conversion or maybe just TwEECer it.
With my couple of bolt-ons I kept door-door with an '04 F-150 Ext. Cab FX4 with the 5.4 3 valve the other day. It's a buddy of mine, we ran trucks out of boredom while the car was in pieces....