Yes, definately rough up the area where the blocks will be glued.  While you are at it, sand the entire area in preparation for the varnish/paint that will go on later.  Do the same with the inside (side towards the hull) of the inwale.  Go back and reread my reply to your post on 5/10.  Following that sequence will save you the hastle of trying to coat/sand the openings in the inwales.  If you look at this pict, you can see the entire inside of the hull is sanded almost ready for varnish.  It is MUCH easier to sand before the inwale goes on.  You can see where I wiped up squeeze out under the blocks.  That area will be sanded before I glue the inwale on.  You will still have to paint/varnish those openings which is a PITA.

   Thanks Mark!  I was trying to cross reference the post with the clc instructions and it just left me guessing as the instructions don't mention it and the pics don't show any sanding. Guess I'll hit up the hull in that area tonight with the sander before glueing up. 

   The steps you listed in that other post, when you coat the rail with epoxy are you letting it cure fully before glueing to the blocks?

   Short answer from my phone.  Do you mean the inwale rail?  If so, Yes, coat, let cure then sand in prep for either glue or varnish.  Do the bottom of inwale rail also.  Easiest to coat and sand any place that will be harder to do after assembly.

   Ok thanks! I got the blocks on one side last night. Not enough clamps for both sides but learned I should use painters tape on the next side to make cleanup a lot easier. Goat rodeo indeed pic here https://imgur.com/gallery/76r7s0y