There are tons of options for suspension but it depends on what you want to do with the car I.E. race it, daily driver, fun toy? Interior you can swap out to aftermarket bucket seats or just recover originals (I prefer two toned seats). That 289 can produce a lot of power especially if you bore and stroke it to 331 or 347 ci with some aftermarket heads intake and carb. You can upgrade to a roller cam setup as well. There's the 5.0 option too if you want fuel injection and the option of adjusting the computer.There are plenty of conversion kits out there and several members here that have done the 5.0 swap. The 67 has room for larger motors as well. There are many possibilities for these cars.
Good luck and post lots of pics.