Do you really want to sell one of the iconic, all time best trucks ever, for a 4Runner?
If you want a 4Runner, buy it. It's a great SUV. But an 80 is the real deal, never to be duplicated, package of luxury SUV, SFA, Full Float rear axle, fully linked suspension, heavy duty transportation that basically, you can't buy anymore, at any price. They aren't going to make any more, and neither is anyone else. Not that you can buy, anyway.
A 4Runner is a great truck. It's comfy, reliable, decent, mass produced etc, but it will never be a Land Cruiser. It will never make economic sense to make this trade, and you'll be trading for something that is nice, perfectly adequate, but inferior. And you already own the 80! Don't do it.
The 80 isn't even my favorite Land Cruiser, and still, you shouldn't do it. It's like trading a Ferrari California Spyder for a 2006 Corvette.