I have a 86 gt that is in need of a serpentine belt replacement . What is the easiest way to get to the belt ? The top , bottom , or through the passenger side wheelwell ?

I attack it through the top. I also have a Dodgerunner auto-tensioner installed, which is worth its weight in gold.

As you have to loosen the alternator, thru the wheel well is easiest unless you have a lift. I'd also recommend the Rodney Dickman alternator reinforcement bracket and either the Dodge Runner tensioner or the Rodney Dickman idler pulley.

I drop them in from above, letting the new belt hang from the water pump pulley. Then I go down below and route it onto the alternator and crank pulley.

Belt bad often side effect of other problems...
See my Cave, Serpent Belt

To install/tighten the alt...
Make sure both bolts have clean heads etc. But lube long bolt shaft w/ anti-seize or silicone/brake grease so don't get "rust" problems passing thru the alt body.

All Bolt heads and other flat spots keep alt tight and lube and crap there lets alt to rotate and belt gets loose.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave