Stan,
There are several problems with quoting the times from the popular magazines of the era. The biggest was the simple fact that has been proven many times over the years.

The car company with the biggest advertising budget with said magazine always would run the fastest times. Sad, but, true. They didn't have to work hard to do it, at the magazines, either. Just run the car from the guys with the small ads in the magazine on friday afternoon, when it was suppose to be 95 degrees.The Chevys and Fords were run at the lower elevation track, on a cool morning.
Sometimes that had a secretary or delivery boy make a pass or two, and averaged the times.
It was crooked, Stan. And, you should have known about it by now.

Most guys who bought a car to race, did it on the weekends, and ran until they were bumped into the next class, at which point, they had to cage and tub the car to continue being competitive. Most, didn't do that-they also drove the car to work. Sooner ot later they figured out the money always won, regardless of brand, and that was that. But, a few modifications went without saying, and times would be faster than the magazines best times, without question. Typically, headers and slicks.

The pure stock drags that were put on by the former Muscle Car Review magazine came a lot closer to the truth, because the owners raced their cars, and the magazine had no vested interest in the outcome. This is why you see the capabilities of the higher engine option of the Buick GS models, today, when there was almost no mention of them, back in the day-think small advertising budget. But, then and now, you are counting on which cars show up and hang around, and for every 250 Chevelles there might be a 442, and it wouldn't likely be a W30, much less one that was ordered specifically for the strip. You could get an air conditioner on a W30 in 1970, and the cam and carb specs were FAR different between the motor in the AC model and the 4 speed car.
W31s were even less common, and, again, you were likely to see the one that got built on the Cutlass, instead of the F85, which was 250 or so pounds lighter, and showed up on the dealers lot with an automatic and 3:90 open rear end, when the 4 speed and 4:33 limited slip was the hotter setup. Few were ordered by owners, and the dealer had to sell the things they ordered.

It is rather pointless to debate about hot they ran/run from this juncture, especially using the corrupted data from period magazines, when so few of the cars even exist, and we are left with so few examples to compare. I will assure you of one point, Stan-the PHR test you quote, above, for a 1970 Cutlass W31 is, by far, not the best example of that models capability.
When I say "most" of the big blocks, you are forgetting, or, don't understand, that the great, GREAT majority of big block Chevelles were NOT 454s-they were 396s. Most of the GTOs did NOT have Ram Air IV 455s-they were 400s with an automatic. Most of the Gran Sports were NOT Stage 3 cars-they were the standard head and cam version of the Buick 455. Most of the Road Runners were not Hemis, they were 383 cars. And, so on. MOST of the big block cars we saw, back in the day, were just the step up from the small block, or, came with whatever the standard big block was. Which, was a motor a guy could drive back and forth to work everyday, and race a bit on the weekends.
And a W31, or, for that matter, a Pontiac T37, with the right equipment, in the right hands, was more than a match for them. In the real world, outside of the ad directors office at a car magazine, anyway.
I bracket raced for enough years in the early 1980s at Brainerd and Rock Falls to realize just how rare an LS5 Chevelle or a Hemi anything was. I've never seen a legit LS6 Chevelle.
Those are not "most" big block cars, Stan. Sorry.

Best,
Ted