Well, you don't need to remove the engine to get the oil pan gasket replaced, only raise it and lower the suspension. I have done quite a lot. Volvo even sells a 2 piece gasket witch could be attached together like a puzzle.
Anyway, I hope you did not damage the transmission pump.
You need to install the torque converter into the transmission, but inspect the front seal first, make sure it's still OK, if not you need to replace it. Seat the converter ALL THE WAY into the transmission before you install the engine. I hope you did not remove the flywheel with the pulse ring without marking the position. If you did - you are in a big trouble.
I'd strongly suggest to replace the rear main seal and the seal housing gasket also, since the engine is out already, BUT make sure to mark the pulse ring position. The best way if you set the front crank pulley to the TDC position than note and mark the ring's position. It is very important.
When you are re-installing the engine, be careful not to damage the ring in any way and don't break the distributor.
Zee