Tailgate question

[Kixwy2]

Hey guys,

This might be a stupid question, but how different is the 73-87 tailgate from the 88+ in shape and dimension? I ask because I am looking for a black colored diamond plate tailgate cap (aluminum, not plastic) and can only find ones that are meant to fit 1988 and up. Also, since the history on the truck is suspect, I'm not really sure what year the tailgate actually is - I only have the dimensions.

I bought some rails off CL that I modded slightly to fit and they look great. Now I want to finish the look...

Here's a pic of the (newly painted) tailgate - if someone can help me with the year that'd be awesome!
And a pic of the bed rail I'd like to match. Not sure why it rotated like that.