79 C6 pump removal

[greme]

I have a 79 f250 with a C6
I want to pull the pump and replace the O ring and paper gasket.
the trans is still in the truck. i removed the 7 bolts but i cant get the pump to pull out, but it will spin and wiggle.
is this possible with the trans still in the truck?
is there something internal holding the pump in?
thanks

[Fraser]

If you remove the pump in a horizontal position, all the thrust washers behind it will fall out of place. Last time I did it, I hung the trans. from my crane, pump upwards. I threaded two of the holes, and used a slide hammer, but that's cheating, it's supposed to be tapped out from inside.
The o ring seldom fails, a leak is usually the seal, the bushing should also be changed.