Proper engine temp?

It should have a 187 F T-stat in it. One can only guess but I would look at the fan clutch first from what you said.

@ tony rome: sorry, they still made full size blazers back then haha. Your issue is obvious to me, you probably still have the original 2 core radiator and need to swap it out to a 3 core for the V8 engine. I have seen this before where a guy put a 350 in a S10, it wasn't very pretty :)

First, the electric fan always running is stupid, but nonetheless...

The thermostat should be 195*, it was the universal temp used for the SBC motor. If you can't keep the motor at 195* cruising, your radiator is inadequate. Never buy used radiators, you cannot tell how they are inside without a flow test.

210 is good. Pretty much what engine temp should be at

210 is not too bad, but still of concern. Its funny how people will point to all the cooling parts at fault when overheating and forget one thing. If the timing is retarded by only two degrees . . . . .

Check it with a good timing light, vacuum disconnected & plugged.

There is no fan clutch, just an electric fan that always runs.

Try straight water with "water wetter". Water cools better than antifreeze. If it never boils, the temp is fine.