84 Chevy K5 Blazer Overheat and timing

I have been helping a good friend on his K5 Blazer, and it seems to have overheating problems. we have been fixing someone elses mess on this one. The guy that my friend got this rig from was an RTV fanatic, and used it on everything. We have cleaned up most of it, but the intake manifold was sealed with it from the looks, and we have not gotten it off to inspect it yet. We have had trouble timing this rig, seems like it just doesn't run right, even though we have tried everything. I am thinking the carb is dirty. Anyway, this blazer has a 350, and run at about 210 deg. F at idle. We have flushed the coolant, changed the thermostat, and still running hot. If the timing where off, would it make it run that hot? I know if it is too lean, it will make it run hot, but this seems exessive. The temp never seems to run over 210, but it worries me. The guy that used to have this blazer put in an edelbrock performer intake and carb, CFM unknown. When the guy put in a new distributor, he had it in 180 deg out, and wired the cap to make it run. We got the distributor turned around and wired right, and it runs, and sounds decent, but backfires and stumbles when accelerated. Makes me think the timing is still off, even though the thing idles good on a light. Any help you SBC guys can give would be great! thanks.

You may want to check the radiator cores,,,make sure they arent plugged.
Also check for Vaccume leaks.