Just inspected the range on the tensioner. It is pretty much at the end. I'll go ahead and pick up a 1" smaller belt and try it out. It should work out just fine.
Okay - went to Advance, got a 89.5" belt (Drive Rite 895K6, prt # 5060895DR) instead of the stock (w/ factory A/C) belt which is 90.5".
Swapped alternator pulley back for stock and put on the 1" smaller belt. PERFECT! The auto-tensioner range shows it is about mid-way, so it is fine.
With the stock pulley on, gauge inside shows voltage much higher - even with A/C on high, lights and fog lights on, interior lights on at idle, it still has a higher reading than the underdrive alt. pulley did with nothing on, just idling.
Now if only I had just bought an even smaller belt, that pesky smog pump....oh well, thanks for the input guys.
Regarding the belt tensioner,I noticed on my 89 that if you remove the belt and loosen the tensioner mounting bolt a little it will move up and down a bit,so positioning it down as far as it goes and tightening the mounting bolt can give you a little more tension on the belt if it`s not already in the lowest position.