R,
Check for a clutch inspection plate that may need to be removed. I am
not familiar with that particular application but it did stop me on my
first engine pull.
Sparky

If the 1.6L in my 87 Sentra is the same as yours there isn't a
removable clutch inspection plate at the base of the bell housing that
needs removal.  I don't recall any hidden bolts.  You might try rocking
the transaxle side to side and then up and down to see if the bell
housing surface is separating slightly from the corresponding engine
mating surface.  If the two are dead locked, then maybe you've missed a
bolt.  Otherwise, the problem is that the transmission input shaft
splines are stuck on the clutch disk splines.  The transaxle must be
supported with some kind of jack or blocks that prevent the transaxle
from sagging relative to the engine.  If it sags even slightly, the
splines will jam.  The transaxle needs to be supported while you rock
it around and simultaneously exert backward force while insuring that
when it breaks free it doesn't fall on the garage floor.  That's
precisely the step that makes transmission removal such a joy!
Alternatively, though much less likely, the pilot bushing could be
seized on the end of the transmission input shaft.  If so, I'd expect
you'd have been hearing some nasty noises while it was running.  A dab
of grease in the bushing when you put it back together is good medicine
to preclude such an outcome.  Good luck.  Al

If you have checked and rechecked for that last bolt you may have
missed, then hook up your clutch actuator (cable or slave) and push the
pedal. This is enough to pop the trans loose without it going too far.
CAUTION- If it is a slave unit the slave piston MAY pop out if it moves
too much, depending on where its mounted.

-SP