does it have noids on the VB?
does it have a wire/sender hook up on the back of the cast by tail housing?
those would be elect lock-up
early lock up 904s like I have use hydro pressure to lock-unlock the TC.
IIRC you could swap out the VB for an early one to ditch the wire hook up on it.
as far as 904/999??? does the tailshaft have the cover for snap ring on the side or on the bottom...on the side it is a truck unit and may be a 999
get the #s on the pan rail and I will see if I can find it on my trans ID list.