Leaking transmission

Well if it's coming from the BH and it's trans oil, then it would have to be the front seal. It's a bit-O-work but $20 should cover it.If the trans is otherwise working,I see no problem with slamming it back in. But before you do check the convertor hub for cracks in the corners of the pump-drive slots.
But I suppose you should be informed that the oil could have just come out of the vent which is also in the BH. If for some reason the trans was overfilled or if the convertor drainback checkvalve had failed, and you perhaps jacked the back up high enough that the oil just spilled out of the vent;well then nothing is really wrong,well other than the high, or temporarily high, oil level.
So then you might want to give it a good wiping, then let it stand for a few hours. Then with the engine off, check the oil level. It should be a little low,not 6 inches up the stick,lol. After the level has been thus checked,put on the park brake,start her up, put her in Neutral, and let her idle for a few minutes,then read it again. It should be normal to a bit low with cold oil. You may have to dip and wipe several times to get a genuine reading. You did put on the park brake right?

IIRC; pre66 valvebodies did not have the drainback check valves, so a high oil level after sitting for a few hours would be normal.