If you go to a parts store and tell them you have a 86 C10, the only radiators that will come up are the small ones. Being that most of the people behind the counters aren't 73-87 fans, they probably wont know what you are talking about when you say 4 core.
The trick I used is to ask them to pull up a radiator for a 1 ton crew cab with a 454. That should bring up the part number for a 4 core radiator. Make sure you take it out of the box first and check that it's the right one though. It's actually the same price as a smaller radiator, at least at Advance Auto Parts where I got mine.
The aluminum one cant hurt though. Long as it's a quality piece. Though a lifetime warranty is nice, if my coolant is all over the road and I'm stranded somewhere the lifetime warranty isn't helping.