Looked through my pictures of unrestored 68 FE powered examples. The vast majority (over 80%) had the bent or curved pipe design on them. Next step would be to see if this was a running change where the part was changed part way through engine production for that model year
Would take a fair amount of effort to post all the pictures of old, crusty and in some cases partial views. Maybe if I can find time a list of VIN's might help convey what I found