Have you measured the length of the boom tube, from center-to-center between the two bottom brackets? If not, you might want to check that to make sure just how long that stoker compartment is. As noted in your other thread on the belt, I'm thinking you've got something less than 28.5". You can usually double check the length at the seat tubes since many tandems tend to use parallel seat tube geometry, e.g., 73° front & rear, and I think Calfee's fall into that category unless they are for either very short or very tall teams.