Looks like yer oil pan is toast. It may have been improperly used as a jack point,or the motor was put down hard,maybe hit a speed bump or something. Sometimes aluminum parts can appear to be cracked and not be,I dont think thats the case here.
Removing the head was not necessary as
@GIXERHP pointed out,because the Busa motor has a crankcase that splits horizontally. Motors split vertically as well,that when you need to take the head(s) off.If you have a trans issue on a Busa,not much needs to come off up top,you go at it from the bottom. I wouldn't worry about it now,that ship has sailed.It's a shame you did all that extra as your motor was running fine and is a low miler from the pics you have posted. Manuals are awesome,a must for somethings,but asking here will help too. Most of us have time and patience,its all good.
Its personal preference I suppose,but over the years I've favored Clymer manuals over Haynes.
Rubb.