318 overheating

There is a test kit for combustion gases. Thats where i start. No gases, then water pump. Then rad. If you can see inside rad with a good light, look for blockage.
A good telltale is the air passing through rad should be hot, like a furnace if rad is doing its job.

poor heat from heater, in warm weather, the heater should be unbearably hot. Heater fan on high, if core is working properly hoses should be near the same temp. Plugged core, big difference in temp.
If core is plugged, good chance rad is too.