Hi Snowtoy,
I don’t want to run tires smaller than 31s, so there would be no point to buy or borrow a set of smaller tires just to dyno test.
Gnarls. 
The reason for testing w/a set of stock tires is to verify if the .020 bore/cam/header/exhaust upgrades equal/surpass the rear wheel hp/trq of the w/31's, my guess is it wont, and the on highway performance gain/$ spent you are expecting wont be there either.
I re-read your comments and you indicate that there is POWER loss or gain with gear changes. Perhaps its just semantics?
Its my understanding that changing ring & pinions to lower the gear ratio or changing tire sizes which affect final gear ratio, has zero effect on the torque or horsepower numbers produced by the engine. Changing gear ratios will only move the torque and HP numbers up and down the RPM range.
For example, the result of changing from 4.10 R&P to 4.88s when going from 28" tires to 33" tires will have a very noticeable "feel" of power increase because the gearing will put the higher torque number in a more usable RPM range.
I could be totally wrong - and if I am - please explain. 
Gnarls.
Gearing has no effect on crank output numbers, where it does effect the numbers will be at the rear wheels, the only place hp/trq numbers matter in the real world. Most stock drivetrains tend to consume 15-30% of the crank output, smaller gears than tires will absorb more torque as it takes more energy to turn them, where taller gears than tires will absorb less resulting in rear tire performance gains. An example of this is the '85 2wd I took in partial trade for 4 Runner I had restored. The PO had used the truck for work and towed a 5-6k lb trailer with it. After replacing a few clutches and stock diffs, his mechanic suggested going w/4.10's. W/the 4.10's the truck would chirp the the tires in 3rd gear up shifts at when driving aggressively. There was no change to the engine, yet it performed as if there had been a larger engine installed, it was very fun to drive, though a bit noisy rpm wise at 75mph.
As you know Toys are heavy and the older gens had small engines, IME gearing has always had a better bang/$ result than engine upgrades, outside of complete swaps that is, maybe yours will be different.
