will a chevy astro 1994 rear end fit in a 2,000 gmc safari SLE w/AWD?

[SaveAmerica]

The rear end in my 2,000 GMC Safari SLE is making a fairly quiet constant whine(in rear end) ,I spent almost all my money on the van.The person I bought it from didn't exactly tell the truth about many things with itI replaced the rear brakes,because mechanic said he thought that was it.A friend can get a used 94 astro awd,but I can't find any info as to if it will fit.If you know, are many other parts interchangable?Ie tranny etc.?Also someone said increasing grease weight in rear by five pounds would quiet it down is this advisable?Thanks for any help!