It looks like I will have to replace the jib and genoa tracks. When I pulled them up to paint the deck I noticed they are badly corroded on the bottom. Should I use the same length and location? Has anyone repositiond or used longer jib tracks?

If you're at all interested in one-design rules, 5.4.6 specifies the location of the track.

I've replaced my jib tracks with the same tracks from Schaefer, with twice as many holes. Haven't changed my genoa tracks yet. Will probably remove them over the winter, and drill several extra holes.

I'm not too worried about one-design. There is only one other j-30 on the local lake. From the lack of responses I assume there isn't any advantage to lengthen or move the tracks.
You might have some trouble drilling holes in your track. The anodizing is hard and dulls drill bits fast. You might want to try one hole before taking the trouble to remove the tracks.