is it possible to install pre-bent transmission lines with the headers on. if not is it possible to get different lines so i dont have to take the headers off?

Sure...I replaced the prebent lines on the TH400 in the '67 just recently.
Did it on a lift and routed one line at a time starting from the front. All I did was disconnect the battery just in case the tubing crossed something...

I just did this too. Had to bend the lines over one of the header tubes near the starter. Didn't need to remove the headers. The difficult part was wrenching on the trans fittings up in the tunnel with the header tubing in the way.

thanks gentlemen i was trying to do it from the trans forward i will give it a shot going from the radiator back