I just finished installing a two piece trunk in my 74 cuda. You can make it look fine if you take your time, I was concerned about the center seam, but most of it is covered anyway by the tire hold down and the trunk latch support.
Pro's of the two piece for me were; Ease of handling, I had this trunk in and out about 20 times before I welded it. RR trunk is much bigger than the cuda one, I know because they sent me that one by mistake the first time.
Price, I bought this for less than half what a 1 piece would cost.
Cons are, you have to weld the seam. Not sure with the RR but on mine I hade to weld the tank supports on the bottom. The drain holes and access holes to the shocks are not drilled out, easy fix. and the two piece panel does not extend to the tail panel on the cuda, so you have to make a piece to connect it. I would do a 2 piece again if I had to.