The 4.0's will have decent crank, rods, and pistons, like almost all Ford pushrod engines. You can do a lot with some parts, but the pistons should be changed during a rebuild.
The rods in a 302 aren't terrible either, but the cost of aftermarket rods is so good that you change them as a matter of course now.
See if you can get an aftermarket set of rods for a decent price, and spend good money on strong light pistons. The SOHC has high enough compression that not too much boost can be used. For serious power you'd want a lower compression like stock 302's have.
James, what kind of rpm's has your engine seen? Has it all been normal rpm's which aren't much past 5500? The higher rpm's wear out the valve springs much faster. That's why a lot of 302 Mustangs smoke etc, the five speeds let the driver's spin the engines too fast, too often. My first 91 LC never smoked, even at 112k miles, it was an automatic. Night,
