I did the muriatic acid and wow does it work good. My radiator looks new on the inside now.

I filled the rad i would say 1/3 with water and then with muriatic acid and let sit for 15min. then I flushed really well with a water hose and shaking as best I could. Then repeat. The acid does a number on the paint on the outside though so i just repainted it with some black high temp paint.

I will post back and let everyone know how it works out for me.

88 Montero, 2.6 Black