Definitely a US-made frame.
All their frames were made in the US until 2009. This tandem predates this by well over a decade. BTW, Cannondale serial numbers usually have the date code within them, so you can probably determine actual production date.
The biggest challenge you'll encounter is removal of the existing freewheel. They get incredibly tight on tandems. And if not properly lubricated when installed, it will be a bear! I wouldn't be surprised that you'll break freewheel tools, and have to disassemble it down to just the bare body to clamp it in a vise for removal - or worse, cut it off with a Dremel. But one recommendation is to apply quick high-torque forces during freewheel removal, not just more and more force applied to the tool. This saves freewheel tools, especially Suntour type.