904 vs 727?

If it takes 12% of the power to drive the 904 and 18% of your power to drive the 727 then you have a 6% loss between the 904 and the 727.
If I remember correctly in my old age the 85 and 86 lock up Transmissions used to fail pretty much straight from the factory. What the dealership in our town used to do was plug that lock up on the valve body and do away with the lock up function. Then you just had first second and third like a normal 727 or 904.
There was no wire for the lockup it was hydraulically done through the valve body.

And no there was no low gear set for the 904 back in 85. However you can take a set and put in that transmission from a more modern transmission.