X 2 on pulling the freeze plugs for a good look. You never know how the PO cared for the cooling system. Because of mild overheating issues I took mine out and found a coating like plaster and barnacles all around in there. The P.O. was known for scooping up swamp water to refill after a boil over. Also were deposits of that aluminum powder leak stop. It was a mess and that was after all kinds of flushes. Here's what I did for a super flush. I found plastic plumbers test plugs that fit the freeze plug holes so I could easily put them in and out and get a good seal. I removed the T-stat housing and water pump and made blank off plates with brazed on garden hose fittings and adapted the block drain to a hose fitting. I got one of those small 120v pumps with garden hose fittings built in. I cut up some garden hoses and plumbed it so the pump would suck out of a 5 gal bucket and pump into the water pump plate. Hoses from the T-stat plate and block drain ran back to the bucket. Sooo,,,,,,, I could now circulate my flush of choice through the block and not hurt my brand new radiator & water pump. I could easily pull the test plugs and check on my progress after each flush. I found that no radiator flush I tried would touch the deposits. I even ran an industrial HVAC scale dissolver though there with minimum effect. I had to fab up scrapers to go through the freeze plug holes & physically chisel it off the cylinder walls and made curved ones to reach around behind them. I tried diluted muriatic acid and it had some effect so I finally ran straight muriatic acid in there for 20 minutes. That's when the pump impeller gave out but it did the job. I had clean as new looking cast iron in there. Now with a 170 T-stat and lugging though the mud for hours towing a loaded trailer in the summer high 90s I still can't quite hit 180. This maybe extreme but it worked and I never would of known if I hadn't looked in there.