318 Overheating...Help!!

I had a friend of mine with a 73 Dodge camper van (also a 318) that had an overheat problem; one day it started seeping out a freeze plug. so I popped that one out (above the starter) and the block was FULL of scale! I popped out what other freeze plugs I could w/the eng in the van and took a nozzle on a garden hose and flushed the crap out of it, overheat solved; BTW; I definitely would not call 210 "overheating";
something else; I have had engines seem to "get hotter" just by changing the temp sending unit.

On my 78 Fury, also a 318,(47K orig miles, I'm the 2nd owner) I changed the waterpump right at 40K; (thought I had a bearing squaling, wound up being the alternator) but I took out an 8 vane waterpump parts store sold me a 6 vane unit saying the 6 vane had more room for fluid, the extra 2 vanes were an "impediment" to flow; Bullcrap; Just that change alone and my engine rus a notch hotter ("1/2 gauge" used to be 1/3 gauge full hot) than it ever used to. I'll take the vane one next time, thanks.