Flushing a radiator that might have also been a critter house

The CJ5 that has lately been doing everything it can to make me swear off all things mechanical forever, developed a radiator leak while just sitting in the garage.  A nice 3 inch crack with a high pressure spray coming out opened up along the bottom the day we were going to try and make it move under its own power for the first time in years.  

So I look around, decide to roll the dice on one of the plentiful and cheap aluminum radiators all over amazon and ebay.  Well.... I doesn't fit.  There were a couple problems but the biggest was the bottom hose fitting is at sharper angle making the lower radiator hose a friction brake for the power steering belt.  

I have an older radiator that came with a parts pile that is supposed to be good.  Looks like it had some minor seepage but it appears to be in "ok for now" condition.  The problem is when I pulled it out of the shed it looks like something was living in the bottom of it at some point.  (In my head it is a mouse named "Johnny Low Range" with a lot of love for the lady mice and an appetite for adventure)

I want to flush this thing out as best as I can before install.  So I am thinking lay it flat, dump some boiling water in it, let it sit an hour or so, then hook up the garden hose to it and let it run for 15-20 minutes.  Seem reasonable?  I need to dig around in the garage but I don't think I have any Simple Green type cleaners and going to the store for some probably isn't the best idea right now. 

This thread is more a thought exercise than anything.  How would you clean out a moderately cruddy radiator?

Artist interpretation of the critter that may have been living in my radiator-

In reply to logdog :

That's probably find if you're just trying to clean up after Johnny Low Range.

I've heard a lot of good things about Thermocure from Evapo-rust if you're dealing with scale leftover from his lack of bladder control.

CLR and water.  Let it sit overnight.  Flush well with a garden hose.

Quoted just because  

(In my head it is a mouse named "Johnny Low Range" with a lot of love for the lady mice and an appetite for adventure)

I've seen what mouse pee does to metal and if old JLR peed in that radiator, it's not long for this world.  Mouse pee ate through an intake valve, valve seat and a piston in an old "mouse" motor I was tearing down...