Answered my question this morning. No, even with the fan off on the 4.3L there is no room to fit a radiator.
Now to blow the truck back apart and set the drivetrain back
I did check the motor mounts and the conversion kit. I'm assuming these plates get mounted to the frame and then I use whatever existing mount is on the engine. One thing I noticed on both sides: The passenger side has the water pump housing in the way of it being able to move backward and the drivers side has the oil pump I think. Either way, I think the idea of using V8 mounts swapped might not work out. Today is quickly becoming a "I told you so" for JoeD