How to remove the bull gear from an automatic transmission

["Michael & Laurel Eppinger" <epp@domain.elided>]

IH all,
How in the *&$#@$$% do you remove the bull gear from the rear of an AT?  I
want to install a dana 300, but I have to remove the dana 20 bull gear that
mounts to the back of the extension housing on the at.  Is it reversed
threaded?  Or am I not applying enough force to the breaker bar?  My impact
wrench would not budge it.  I have the tranny installed to the engine, but
I don't want to apply to much force to it, for fear of breaking something
internal.  Is this a worry?  I guess I could put the breaker bar on and put
a hydraulic jack under the handle to apply an ungodly amount of force to
it.  Would this break anything?  I need help.  Is there a trick to this?  I
am at a standstill till I get the gears swapped.

Epp