the caprice waterpump pulley will not work with the 4.3 waterpump pulley. the 4.3 pulley mounts closer to the waterpump. the 4.3 pulley is longer. maybe a corvette pulley will work it is a 5 1/2 inch diameter but i do not know.
i just went to the junkyard today. i take of a water pump pulley off of a 4.3 s10 with serpentine and it measured 5 3/4 inches in diameter, if regular 4.3 serpentine system is the same as a typhoon or syclone 4.3 serpentine system it will work.
Smaller water pump pulley for 88-92 Serpentine drive sys.
http://www.thirdgen.org/techbb2/showthread.php?s=&threadid=245263&highlight=waterpump+serpentine