My '88 had a radiator from L&L Products, aluminum, it fit under the support, towards the front about four inches and gave a little extra space on the front of the engine.
Never had a cooling issue and really pushed the engine sometimes.
Did run into a problem with the truck lifted and all of the air dam $hit removed; on the hy-way the temp would go up but not boil over.
I lifted the rear of the hood about 1 inch and all was good.
When I removed the air dam the air that would have moved under the truck actually stated coming up in the engine bay but only at hy-way speed. This would stop a lot air in the bay, blocking some of the air through the radiator.
Funny when the hood went up and the flow was restored all was well.
Where am I going, L&L Products had a great radiator.