Is there any way that the
low gear planetary out of a 904
could be used to replace the
planetary gears in a 46RH overdrive unit?

As i understand it,
to create the
0.69 ratio overdrive unit
in the 518/46RH/46RE
Chrysler engineers re-used the
1.45 ratio planetary gears out of a 727

1 divided by 1.45 equals 0.69

a low planetary set of 1.54 would create a
1/1.54 equals 0.65 overdrive ratio