Car getting real hot....
Just a few observations. That fan is a turd. There are a LOT better choices than that tiny blade flex fan. Next up is that shroud. It's blocking too much of the radiator core. Another way to describe it is, it's too close to the radiator. You need more air space between the radiator and shroud, OR you need to cut some holes in the parts that are blocking air flow to the rest of the core.
Finally, the 13 pound cap. That's designed for a stock radiator with a stock engine at a stock power level. Not one that's producing more power than stock. I would upgrade the cap to a 15lb, either cut some holes in the shroud to expose more radiator core to air flow, or move the shroud back away from the radiator for more space and finally put a GOOD fan on it like for instance a Chrysler 7 blade or the staggered 5 blade fan. Doing those things will very likely solve any over heating issues.
All that said, a somewhat related story.
Kitty and I went to Macon today in Vixen. First time we've driven it that far with the new engine. From Jones County to Macon, to Gray and back out to Jones County where we live. Probably about a 75 mile circle. Or triangle....or what the hell ever. lol
It was HOT today. Got up to like 97 with over 50% humidity. We probably should have taken the Escape, but Vixen hadn't been driven in several days, so we took her. Got into Macon and as usual stop and go, stop and go. Picked up the stuff at the machine shop and we decided to stop by Nu Way for some hot dogs for lunch. Five cars back in the drive through, so I cut it off. Finally got up to the window, got our stuff and started home. All this time the temp gauge only got to the 1/4 mark. It was a little warmer today than it usually runs. Normally it runs barely 1/8 the way up. It also didn't cool back off to the 1/8 mark on the way home on the road where it usually runs. This is because it reached the point to where it got "as hot" as it probably ever will rollin down the road. We took it back out tonight, because I had men's chorus practice in Gray at 7PM. By then it had cooled off about ten degrees and she was back to her 1/8 way up self again.
Now, there are several more things I plan on doing to help....not that it needs it, but the cooler the better, so I'm going to do it. That includes making some panels out of sheet metal to close off all the holes behind the radiator support under the car in the K frame. This will stop air flow from going up into the engine bay from the bottom and avoiding going through the grille. I also plan to add a small air dam like the ones on the 69 Z28. This will push air out front, making the air that was going under the car, go through the grille. I also have a hard to find 5 blade staggered blade solid fan I am going to put on as well. That will move more air at low speeds and cool it off some more there too. I WISH I could find an early A body slant 6 fan shroud, but good luck with THAT. lol Again not that I'm hurtin with engine temps by a long shot, it's just that any little thing you can will help. All you have to do is look at any newer car and they all have those mods done. So don't give up on it, because there's lots of stuff left you can do.