I think Dr. Benz--one of K&K's dealers, will concur: the sheet-metal parts from K&K are very, very good.
Without body-shop experience myself, I will say that I don't believe installing any kind of sheet metal or body part is the same as mechanical. Most mechanical parts simply "bolt in" to place (for installation: adjustment is another issue!), but installing any kind of sheet metal is somewhat of an art--getting everything to line up just right, trimming excess metal, or adding some, welding, filling, painting, etc. is an art.
Note that some of what K&K sells is Mercedes parts--they don't make everything themselves. I bought a Mercedes hood (Bonnet) from them during the restoration, other sheet metal parts were ones they had made themselves.
Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored