Flushing a engine block that has been sitting.

[Tony_H]

I have a 67 Fairlane in my shop with a 390 that has sat for twenty years. It appeared to have very little antifreeze in it with big chunks of yellowish solidified looking coolant in it. After some flushing, a new H2O pump, radiator and hoses, 2 different thermostats, new fan clutch and factory shroud. It wants to heat up to 230 going down the road. My temp. gun indicates that it isn't circulating but maybe a little. I suspect the block is plugged up with sludge. One of the forums suggested CLC for cleaning sinks and such. What do you guys think? I also want to swap out the O'rielly's H2O pump for a high flow Stewart or Flow Cooler pump.
Thanks