Overheating at idle?

[MN Stumpjumper]

I just got a 50 2 door sedan with a stock v-8. It runs good, temp gauge shows 160-190 out on the road. When I stop and let it idle, the temp rises quickly. I didn't let it get past 195, as soon as I start driving, the temp goes down.The PO had the radiator rodded out.
Any ideas to start diagnoseing this problem would be appreciated.
This is my 1st flathead. Thanks.