Thanks to those who have posted on this - I really appreciate the help.

Maybe things went ok - hopefully someone can tell me whether I goofed. I wasn't sure what a torque converter looks so try not to laugh when so you read further.

My son and I removed the 6 bolts holding the engine drive plate to the starter ring. This appears to have been all that was holding the ring but I could not actually dislodge the ring even at the completion of my work. We then unbolted the starter (which uses two of the engine/trans bolts) and all of the other engine/transmission bolts. I had the engine and transmission independently supported and we separated the two. As we struggled with the starter ring, I eventually found the object next to it (which I thought was a flyweel mass) had coming away from the transmission shaft. This item is a heavy metal doughnut - capped on the engine-side cavity and with a spline recessed in the center of the transmission-side cavity. The spline cavity is filled with transmission fluid and mates to the transmission shaft (The transmission shaft has a ring onto which mate the two tangs (I think 'jim16671836' described) on the end of the doughnut spline.
I've heard it is a big deal (near impossible) to re-assemble a torque converter back into a already assembled transmission. It doesn't look hard at all to put this doughnut back onto the transmission shaft.
Is this doughnut the torque converter or the flywheel? Is there anything special I need to know to re-install it in the future?