Not sure if it is the same for a 68', but I ran into this problem when I went from the original single exhaust to dual exhaust on my 65'. There are different dist. blocks that mount on the rear axle depending on if the car came with single or dual exhaust. The location of the bracket for where the hard line running from the front meets the rubber line that goes to the dist. block was different on a 65' as well. For a single exhaust the bracket was more towards the driveshaft and dual exhaust is moved further away from the drive shaft moving it further from the exhaust. The brake line running from the master cylinder to the back was also different, when I installed the correct one for dual exhaust it was clear where the bracket needed to be relocated back there due to the shape and bends of the line. Hopefully someone with a 68' can chime in...