BELT #
 

WHAT SERPINTINE BELT # OR SIZE FOR A/C REMOVAL ON 89 5.0

i am not sure, but i just use a string and rout it around the pulleys without the A/C. and mark the string. lay it out and measure it. if the parts store doesnt have belts in inches (just metric) multiply the inches by 25.4 and you get mm.
try that it should work. if the water pump gets in the way. you must buy the A/C idler pulley. a shoreter belt just wont work.
i used this technique today as i was eliminating the smog pump.
i hope it works out for you!