This took me ages to get started on, even with the hint about CLAM-S, which set me off up what turned out to be a blind alley. It does all come together eventually, but I found I had to start at the top and work down before the thematic treatments fell into a pattern.
Dryden, the bottom row isn't one of those thematically affected, so that should help a bit. The weaknesses seemed to me to be the two missing vertical bars (essential in the final grid as described but distracting during the solving) and the fact that the fifth row contains an exceptionally well concealed thematic item that you can complete the grid without needing to identify. But a bit of Googling (or a long memory) will reveal it if you're a complete-ist.
There are some clever teasers in the clues, alluding to both elements of the theme.