As for doors, 68,69,70 dodge coronet, Bee and 68,69,70 Plymouth Sat., Road Runner are all the same body lines. The only dif. is the 68 has the door lock hole at the end of the door where as the 69 and 70 are a few inches from the door edge.
If you do change your front clip, now you would have rectangle reflector sidemarkers in the front and the round side lights in the R Qtrs.
Also the trunk lid is different from 68 to 69 and I think the taillight panel is different so don't think you could put 69 tail lights in it either. I would just do a 68 coronet RT clone and keep what you have, If you ever want to sell it, would be better all 68 than a Mixed Breed.