my 740T has developed some belt squeaking, yet all the belts are fairly new, the tension is good. I even replaced the bushings on the alternatora s they were shot, thinking that was it, but its still squeak-squeak.

someone suggested that the crankshaft pulley gets worn out causing the belts to ride too low in it, and this can cause squeaking ... is there any truth to this?

 

Are you sure it is the belts that are squeaking? I have read on one of the forums that when the harmonic balancer starts to fail it slips on the rubber causing squeaking noise until you get a hard failure. You can check to see if the balancer has slipped by simply checking the timing marks to see if they still line up with TDC.

 

To get an exact picture of what you have, use some belt spray individually on each belt. The noise will disappear at least for a while as you hit the culprit. You can also use a bar of soap to run along the edge of the belts as they are turning, carefully of course, and the noise will go away momentarily.
Worn out pulley theory doesn't sound good to me.
The harmonic balancer slipping is something worth checking--the belt "lube" will let you eliminate various possibilities.