You still haven't posted the actual oil pressure you are getting. I would highly recommend sorting out the wiring and vacuum line disaster and performing a few basic engine health tests before doing anything drastic. As Green said, it looks like someone was in a hurry and just didn't care about the outcome. It may be well worth it to take some time, learn what everything is and start cleaning it up. Start on one side of the engine and work your way around.
Check you're actual oil pressure before tearing into the engine.
http://www.cygnusx1.net/Supra/Librar...Section=LU&P=4