I don't think the chainstay is actually removable on this bike -- I'd expect any SWB and LWB changes to happen up front rather than back there anyways. (Based on what I found, the bike can also be converted between under-seat steering and above-seat steering as well. Though SWB and USS is what I've got now, and it's what I wanted, so I won't be making any changes there ...)

(Though perhaps I'm not using the right term for a 'bent. On an upright bike, the chainstay goes from bottom bracket to dropout, and I'm referring to the tube connected to the dropout. But on a 'bent, ultimately the entire frame has a chain next to it, so it's less clear -- is it the chainstay because it's connected to the bottom bracket, or the dropout? I was thinking the dropout, but you seem to be suggesting the bottom bracket ... both make sense.)

As for there being a plate, there is a small plate in front of the back wheel -- the frame splits into the two parts that go to each dropout there. I did look there, but I'll check there more carefully when I get home -- thanks!

Inside the dropouts? Nobody would ever notice them there ... but I'll check. If the bike was stolen, I wonder if the police would find them if I couldn't. Perhaps if I can find it, I'll make some dymo labels of it and put them elsewhere on the bike (along with my name, I guess) like at the bottom bracket -- people would know to look there.