The door panels will work, but you'd want to modify the doors to accept the later armrests, since there will be a large oblong hole on each front door panel for the power window wiring to pass through for the switches. You'd also need new window regulators if you did this, or at least thewiring from the 1980-on car. So, I'd stick with the old door panels. Another reason to stick with the old panels is that you can mount 5.25" speakers more easily with them, because they're flat. This is a '75, right? If so, then the carpeting and the rails are the same as a 240. I'd almost do velour, actually, since that will hold you in place better than the leather will. But, if you do really want leather seats, try to find an '86-'89 244GL and get the seats from it. Front and back, including the rear head restraints...

-J (owner of a green '73 145 with '76 side doors, '81 tailgate, '85 black leather 240 front seats, R-sport instrument cluster, and a whole lot of other items)