Is it possible to swap and or modify
the low 904 gearset
into the OD unit of a 46RH somehow?

The planetary of the OD unit
is supposed to be
the front planetary of a 727
Spun in 1 divided by 1.45 = 0.69 ratio

1 divided by 1.54 = 0.65
Would be a lower numerical overdrive

I have to rebuild my OD in my 46RH after 190,000 miles so it will be pulled soon anyway.

The AA price for 727 low gearsets is $900 plus.