This seems to come up once a month or so. Chris, Luckypabst, probably wrote the best tech article about moving the passenger side valence support on the Pn Zone which is now lost to us.
This is not an attempt to redo that. This is just a bare bones "it fits and heres what you have to do."
The stock 230 radiator has trouble cooling most replacement engines. You basically have two choices once you have swapped engines. Get a 396 1967 Chevelle radiator or get a Summit aluminum one. Both cost about $180 to your door.
You will have to modify the Chevelle radiator with a grinder a little, but not that much.
The Summit, requires you to modify the front valence support of the M715. If you look at the passenger side radiator/valence support on your truck, you will see that it is tack welded to the valence and bolts to the frame at the bottom. You will also notice that there are two holes for a bolt to go through. The one being used and another one about 2" toward the radiator.
The entire plan is to cut that support out of your truck, cut off the hole used before, bolt it back in using the inboard hole and then reweld the valence to the support.
I did this in August 2005. I drove the truck into my shop with the stock radiator, used hand tools, die grinder with cut off blades and a mig, installed the Summit radiator and drove it back out of my shop in about 2-1/2 hours. This isn't brain surgery.
The radiator is Summit # SUM-380328.
Here are some pictures I took of mine last night. Look at the 3rd picture and you will see how the "inside" hole is now supporting my valence. Compare it to what a stock truck looks like and you will see what needs to be done.