360 running hot

I have been running that same rad since 1999. No problems @ about 420hp.
An I.R. gun will be your best friend.
Overheating at speed is usually a problem with heat transfer through the rad,especially if it has a condenser in front of it. The condenser fins could be the problem. With no A/C, It could be restricted core-tubes or separated fins. At 3000rpm the water should be circulating pretty good.
But cruising at 3000, the engine will want well over 40* timing. That's where the Vacuum advance comes in.Without the Vcan, the engine will want to run a little richer.If you don't start the fire early enough, the pressure peak could occur very late in the power cycle and it is possible for the still-burning charge to continue burning in the header/manifold.
That cam at 209* is pretty small (about the same as a teener cam), so the power-timing will need to be carefully monitored to keep the engine out of detonation. If it was mine, I'd probably run a little less initial timing, a little more power-timing,and perhaps bring it in a little later. And then I would install the biggest Vcan I could find. Ima thinking I might try 12@1000 and 34@3600. This works out to .85* per 100rpm. So at 3000 you would be running {(34-12)x .85}+12= 31 and I would try a 20* can on that, to total 31+23 =54* and that should be close. The rest is in the tune.
If you are running open chamber iron heads,she might want a little less Vcan or adjust it to drop out a little faster.The Vcan may be limited or swapped out for a smaller one as needed.
But I just gotta ask;why are you cruising at 3000 with such a small cam? That is a gas-miser cam, and has the potential to pull over 30mpg with an overdrive.And make plenty of torque with a starter gear of around 8to9. That cam would be great with an A500 and 3.55s. The starter would be 9.73, and od would be 2.45.
75mph would be 2200 to 2400, depending on tire diameter.I was able to tune a 600Holley on my 367 to get 32mpgUS;with 10.8Scr (aluminum heads),and with a 223* cam, and an A833/ 1.97 final-drive ratio. I think your cam could do better.