Copper vs Aluminum heater core for 71 valiant

Hey guys
I was just cruising around town with a buddy of mine and we discovered my heater core has some issues. It's not dribbling onto the floor yet but it's definitely leaking and fogging up my windshield. So I need to fix the problem and I hoped to ask for advice.

I remember back in the day for another brand of car that most people said the aftermarket aluminum heater cores sold for replacement were pretty much junk. They don't give as much heat and they fail quick. But since this is a daily driver and I can't have it out of commission... what's the factory heater core? Aluminum or copper? Would it be worth soldering the original if it's copper? Are there any copper type cores out there that don't cost a ton of money? Are the aluminum jobs any good?

If it's a factory copper core then I can plan accordingly and make time to fix it. If it's an aluminum job then I need to look for a replacement. I already found the instructions here on FABO to remove it, so I'm good in that department.

Thanks for reading guys.