[akaKJB]

I'm running the Royal Purple 5W20 weight oil in mine, having seen it recommended by several people on various forums.
Devin - your oil pressure issue sounds a little like one I had right after I bought my '87. It was sort of the reverse of yours - the light would come on and the gauge would stay at the top, moving just enough while driving to tell me that it wasn't a stuck or faulty gauge. After cleaning accumulated road gunk off the oil pressure sending unit, the gauge now works perfectly. Now I just need to figure out why my pressure at idle is so low and whether or not it has anything to do with the clattering noise.
Getting ready to fire her up and give it a good 10 minutes to see if mytrplseven's suggestion works out. I'll report back here later with the results.