Here are some thoughts on the Powerglide issue...
As I understand it, if a car has a three speed automatic available as an option "from the factory,," it is legal to run a different "more mechanically advantageous" transmission with the same number of forward gear ratios as long as it will bolt up with no adapters, and is in the same "corporate family."
An example of that would be a smaller, lighter, 904 T-Flite replacng the O.E.M. 727 in a 1970 340 Duster.
Another would be a smaller, lighter, Ford C-4 replacing an O.E.M. C-6 in a 352 Ford (nevermind about the bell housing.)
In 1957, as most of you are aware, Chevrolet engineering introduced a new transmission that was a 3-speed automatic called Turboglide that used a pair of planetary gearsets that approximated first and second gear ratios in the later Turbo-Hydramatics... something like 2.5:1 and 1.5:1. These planetary gearsets were attached to individual torque converter elements that were a part of the main converter, but instead of being held for reaction by bands, or clutches, they were on sprags. This allowed them to overrun when they got to their rpm limit, thereby "shifting" into the next higher gear without actually applying or releasing any clutch/band apparatus.
For a more complete explanation of the mechancs of this operation, there's a well-written dissertation on the engineering that went into this short-lived aluminum transmission in Wikipedia
http://en.wikipedia.org/wiki/Turboglide by someone who has a good grasp of the operation of this somewhat revolutionary torque converter automatic.
Since it is a little different in operation from other 3-speed automatics, it never caught on with the hard-core Stock and Super Stock racers, but there wouldn't seem to be any legitimate reason why it couldn't be used as a stepping-stone to allow it to be replaced by a different 3-speed automatic in say, a 1961, 245 HP 283 car running an automatic transmission class in Stock or Super Stock.
This might alleviate some the discomfort and wrenching of hands that seems to accompany the conception that the racers who have heretofore been limited to a 2-speed automatic are being "given something" by NHRA when allowed to use a 3-speed.automatic. Replacing a Turboglide with a Metric 200 is simply trading one 3-speed automatic for another, something that is the norm for most Ford and Mopar racers, already.
Disassemble a Turboglide, and you'll find the same sort of planetary gearsets (approximately 2.5:1 for first, and 1.5:1 for second) that exist in other 3-speed automatics. But, instead of clutch packs, and bands, you'll find sprags to deliver the power, or hold the elements of the planetaries in place for reaction.
The fact that there's no neck-snapping "tire squeal" wihen going from one ratio to another doesn't mean it's not happeneing;.. it is... I think they had reliability issues for awhile (I seem to remeber them earning the moniker "TroubleGlide",) and I believe that 1961 was the last year they were offered.
Food for thought on a rainy day...