318 LA rebuild after losing a valve seat

Make darn sure the convertor is in all the way. The face of the TC has to be inside the bellhouse. When that is done, rotate the TC about 20* one way and then change directions I usually can hear the pump drive slamming the pump with a satisfying cluck every time it changes directions.
Actually, I'll go you one better; the four attaching lugs should also be inside the BH; that is to say inboard of a yardstick placed across the BH. Later, after the the engine and trans are married, you will pull the TC forward out of the TC, to meet the flex plate. That flexplate has one offset lug and will only fit one way onto the TC. Prefit them now and mark them in such a way that you can see them from underneath the car. Otherwise you could end up drinking a 6-pack before getting them hitched.