if it's a big 10 bolt==8.5 they make all kinds of gears for it, if it's 8.2 you're right they don't make a 4.30. you can tell which one it is by the nut size on the pinion, if it's 1 1/8" it's an 8.2, if it's a 1 3/8" it's a big 10== 8.5.
Zip.
If it is a 8.5, go here.
http://www.rearendparts.com/product....cat=528&page=1