Torque converter installation error - Missed front pump
Never bolt the torque converter to the flex plate (flywheel) first, then install the transmission.
SO .. you've started to tighten up your 700r4, 4L60 or 4L60e bell housing to the motor and the torque converter has run into the flex-plate a bit too early. Getting those bolts into the back of the bell housing was tricky and you want to save some time by not entirely dropping the transmission again. Here's what you need to do:
Acquire two (2) grade 8 3/8-16 x 2.5" long bolts. Grade 8 bolts have 6 lines on the heads, one pointing to each point of the head. If you have an engine stand, use the ones you have for the stand. Remove the bottom left and right bell housing bolts. Replace them with the 2.5 inch grade 8 bolts (available from Home Depot or most hardware and auto parts stores. If they don't know what a "grade 8" bolt is, you need to ask a different sales associate). Thread the bolts into the motor about 8 full turns (1/2" to 3/4", 12 to 20 mm). You'll probably be able to do this by hand. Undo the other four (or more if you've got an LS motor) bell housing bolts until they're no longer threaded, but do NOT remove them from the bell housing.
Disconnect the flex plate from the torque converter if you haven't already.
Disconnect the drive shaft(s). Push/pull/lever the transmission backwards about 3/4" to 1-1/4" (15-30 mm) or so. Pull the torque converter forward, rotate it a bit, then push it back into the transmission. Repeat until it seats so that you can no longer get your fingers behind it (should be less than 1/2" (10 mm) between the rear of the torque converter and the transmission. This will seat the TC on the front pump properly. This may take several goes, just persist and, so long as you can freely spin the TC, you will eventually get it.
Bolt up the four short bell housing bolts.
Remove the long bolts that were used to position the transmission rearward and replace them with the short ones that belong there.
Voila: Your "oops" is now resolved.
The transmission bell housing should (with the torque converter installed correctly) meet with the rear surface of the block without requiring any force.
Do not under any circumstances use the transmission-to-engine mounting bolts to "pull" the transmission and block together, because if the torque converter isn't fully seated the transmission pump can be easily ruined.
The photo below shows a T-400 bell housing that was broken when the torque converter was not fully installed and the bolts were tightened to draw the trans up to the engine
Another thing to check for is to be certain the pilot bearing has been removed from the rear of the crankshaft. Leaving a pilot bearing in place can prevent the piloting "knob" of the torque converter from seating correctly. This can cause the flexplate to fail and even break the transmission case, as was the likely situation HERE.
The photo below shows a cracked rotor in a 700R4 transmission from a mis-installed torque converter. The small cracks are on the tabs where the converter hub engages.
This next photo shows the side the converter hit the tabs and cracked the 700R4 rotor.