Curious if you have any pictures from below. My stock 273 manifolds are RIGHT on the proportioning valve. Haven’t had any issues in the short time I’ve had it on the road, but I do know I need to address it.
No, no pix of that valve from below. But I don't think yours is in the original place - looking at the hook on the mounting bracket, it should poke into a small locating hole in the frame, and I don't see it. And I wouldn't think the factory would have put the valve so close to a 273 manifold.
But the valve wasn't in the same place from one year to the next, anyway. The one in my 63 Valiant was a couple of inches to the rear of the one in my 65 Barracuda. Why? Don't know. So what I did was just move the Barracuda's valve back some two inches (as I recall), drilling one hole for the hold-down bolt, and a smaller hole for the locating hook. Then, of course, had to shorten the front to rear line the same amount as the valve was moved to the rear (but I just went ahead and made a new front-rear line anyway). And made two new m/c to valve lines, running them well away from the header tubes.
PS: I also had to move the horn relay to where it would clear the dual master cylinder. Just moved it to the side an inch or two.