Some news here.
Without a schematic to guide me, but looking at the way the wires were set-up, it seems there is no real difference between the standard mechanical defrost timer and the more modern "adaptive" defrost control "board"/timer. There are two extra prongs on the "adaptive" control are connected to the electrical wires that power the light bulbs -- for the fridge and for the freezer. Apparently, the number of times the light bulbs come on is factored into the algorithm that "adapts" the defrost cycle in the freezer. Doing away with the "light bulb" connection would seem to be harmless. I would lose the advantage of the "adaptive" capability of the "adaptive" control board, but that won't matter much with the way this fridge is used in this shared house, where a bunch of poor people share the rent, and that fridge is opened and closed pretty regularly, but not excessively, that is, about as much as a normal family would open and close the fridge/freezer doors. I would guess that the standard defrost control "timer" is set for a normal amount of use, and no energy savings advantage is to be gained under such conditions. In fact, the Roper fridge from which I scavenged the mechanical defrost control seems to be set for "energy savings" because the Roper fridge says it is an "energy efficient" fridge. So it seems that there is no need to "rewire" the entire fridge at all to swap-in the Roper's mechanical defrost timer.
Let me add that I think that it would be wise to pay the extra to buy the replacement "adaptive control board" IF I was a person with a job that took me out of the house for days and weeks at a time, where the "adaptive control board" would know that the fridge and freezer doors were not being opened for days and weeks at a time, and it would not defrost as much or as often, saving maybe $20 per year or so on the electric bill. Worth it I would say, but just barely.
Let me further add that it should not be necessary to have a computerized "adaptive control board," and a good engineer could have come up with a mechanical analog version of the "adaptive control board" that would have done exactly the same thing, and cost way less, apparently. (All that would need to be done is have some sort of counter that counts the number of times the fridge door opens and closes between defrost cycles, and once it reaches a certain count -- like 100 door openings -- it automatically advances the unit to the defrost cycle, which seems to be all that the "adaptive control board" does. As simple as the "adaptive control board" seems to be, it could have been made an analog device, but then the manufacturer could not rip us off for a fancy electronic control board. But I am all for electronics, but not as an excuse to rip off consumers. Electronics should be cheaper than analog devices, not 3 times the price.)