I don't know if this was mentioned but Advancing the camshaft timing can yield more torque and mpg some.
Because of emissions, the timing was retarded like all vehicles starting in about 1972.
I recently replaced my water pump and timing chain and sprocket with a very affordable Cloyes Street True upgraded set that allows an 8 degree advance crank setting which translates to 4 degrees for the cam.
OEM chain had slop and timing cover was leaking coolant. New gaskets using black rtv form a gaskets with extra added to the corners where the cover meets the oil pan, fixed all that.
So far I'm happy with it is more torquey from a dead stop. Can't say about mpg because my gas tank and a leak.
1996 E350 Club Wagon 351-w, 116k miles.