It sounds like we have a group consensus on the topgallant -- I also think it feels a bit modern, but in light of ships such as the
St. Ann, not too modern for me to say it's out of period. Though one will note, the t'gant yard of the
St. Ann is significantly shorter than the topsail yard -- while on this rig, they're about the same. In the present case that makes it look more like a 19th-century split topsail, which is probably what's giving everyone the jitters.
Since you're asking, here's my personal recommendation, take it or leave it: Use the current topgallant yard as the topsail yard. That will still give a "tall" rig to your sloop while still looking firmly period-appropriate.
