The Spring Creek drop in that is shown above looks to be the same height as the stock seat. What I don’t like about them is the clamp sticks up above the gunwales. It is not a big deal if you are taking it on and off with need. There are three ways to look at the center seat. Is it to get a third person in the canoe, is it once in a while I want to take it out solo, or is it I want to convert the tandem to a full time solo. For the first two I can see the drop in seat. For the third I say get rid of the other two and put some new thwarts in where they are needed and get rid of that center yoke and put in a proper center seat. If you still need the yoke then make that the clamp on part. 
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