An engine with a very efficient combustion space will have lower exhaust-gas temperatures than one with an ineffiecient cumbustion chamber. Now I haven't said one thing about the air/fuel ratio or jetting. Also, race gas burns cooler than pump gas.
With most single-plane-manifold racing engines, you want no more than a 100-degree variation cylinder-to-cylinder at peak horsepower. (Most dual-planes will be 150 degrees.) Your pre-jetting numbers came in around 131 degrees from No. 1 to No. 5; there are a few things going on here. The No. 1 cylinder has a long inlet runner, and No. 5 is basically right below the left rear secondary throttle bore-it's not uncommon for the inner four cylinders to run slightly richer than the outer four.
Are the cylinder-to-cylinder temperatures out of whack? Not for a stock Strip Dominator manifold. You can improve the balance with inlet-manifold porting, and as you have seen, you can balance the temps with carb jetting. I'd say 89s and 77s is extreme, but if the engine likes it, give it what it wants.
The bottom line is how the engine runs on the black dyno-the dragstrip will tell you if you're going in the right direction. The best performance you find through jetting and other mods will be your new baseline exhaust-gas temperature. After you've found the right fueling, you can use that number to tune as the weather changes. Good luck, and keep going rounds!
If you have technical questions for Kevin McClelland, send him an e-mail at chevyhi@primedia.com.