Spun main or rod..
Your going to have to pull it OR drop the tranny to get it out anyway..so my advise is pull it and tear it fully down..
Sudden loss of oil/pressure and coolant overheat is a prime candidate for a cracked block, head, or blown gaskets..
I'd have the block and heads tanked and inspected at the shop before going on..tossing a crank in there isn't going to guarantee you have fixed the problem..and 2 lower ends are Twice as much cost as one lower end ...
Plus...What kind of crap is floating around the gallery's just waiting to Score new bearings..?
Besides, you want to look at the pistons, valves, Cam, (and bearings) , wrist pins and condition of the cylinder walls Before you decide what path to take.
That's my Nickel's Worth..