Water Jacket crud buildup

[72shortbed12]

I have a 350 out of my 71 I'm swapping into my 72. It was a longblock I bought 7 yrs ago, put 15,000 miles on and then tore it apart to start doing a basic restore (that isn't done). Its sat for about 5 yrs now and I've gone out and started it about 4 times a yr. When I went to pull it I found the radiator has a pin hole and leaked out more than half the coolant. When I drained it it was brown and a lot of buildup came out. Now I have buildup in the water jackets in the heads, intake, and I'm guessing the block. Its not horrible but I dont want to have crap plugging up the radiator. Should I just use some prestone flush treatment or is there something better?

Thanks