If the cylinders are good, all that is required for a 4.5L (4.6L is .030 over on the bores) is a 4.2L crank, shorter rods, and new pistons. However, if you are going that far into the motor, and you think it is in need of new rings, I would go ahead and rebuild it.
With that said, there is a lot more to the stroker than just displacement. You will probably want to get a new cam, bigger fuel injectors, and have it all tuned right on a dyno. I have only done the crank/shorter rods/rebuild, but it seems that my motor really leans out on the topend. If you are just looking for the torque or the chance to say you have a stroker, then you won't need the other stuff.
I did my stroker myself, minus boring the cylinders, but I am slightly mechanically inclined. There are a number of little things to watch out for and be ready for:
87-91 4.2L cranks-lighter (more hp on top, less torque on bottom), harmonic balancer bolts on, throwout bearing is different, stud girdle must be spaced
old-86 4.2L cranks-heavier (less hp, more bottom end torque), snout must be modified for harmonic balancer, throwout bearing is probably different and stud girdle probably must be braced (I ran a newer crank on mine).
I have a lot more thoughts and experience to share on this. If you want, you can contact me via PM. I would also consider building your motor for a reasonable price. Let me know.
