starter problem

I don't know too much about the 4 poppers as I have never owned one.  However on the V6 if the starter shim is not installed, it will have those exact symptoms.  You will hit the key and it will grind. Also if I remember correctly the 4cyl cars use a tail bracket on the back of the starter to keep it at the correct angle.

Have you seen a GM starter taken apart?  It's a LOT easier to visualize how the solenoid hooks back into the fork.

You might have just shoved the solenoid in wrong.

I'll assume that the starter is spinning, and that you can hear the thing 'clack' as it tosses the gear out?

Well - I'm going to say pull the thing out (it's not hard!).
Hook up your battery to it with some jumper cables.
HANG ON TIGHT and stick an old screwdriver from the battery post, to the "S" terminal on the solenoid.
It should go WHACK and engage, with the pinion going all the way out until it slaps into the bushing. 
Needless to say, don't have fingers or anything else in there.  :D

This also gives you achance to inspect the pinion gear and see if the ends of the teeth are worn off.