My friend had an '86 5.0L that had tha A/C removed. If you want to run without the A/C unit in the car, remove the tensioner as well and find a belt to fit. You'll have to use the alternator to put tension on the belt. If you want to run the A/C as just a pulley you can. This will not hurt performance and allow you to use a stock belt. Be sure to disconnect the ac switch right above the pulley to prevent it from engaging the compressor.
Also if you have the money you can check around for an A/C delete. It's just a bracket with a pulley that lines up in the stock location. I don't know off hand where you can get one but Google it and you should be able to find one.:bigthumbsup
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