I cant find any photos to confirm it, but there should be a seam. 109 fuselages (and the 108 and 110) were made in an interesting way, with every second panel being pressed to form flanges, which took the place of internal frames. These were alternated with unflanged panels, flush rivetted to produce a very light but strong component. As the presses would not be able to press a complete "ring", each flanged section would have to have a seam somewhere As there doesnt appear to be a horizontal seam line of the fuselage side, I'm picking that it is underneath. Airframe assemblies ltd at Sandown on the Isle of white have recently made the tooling for 109 fuselages. See thier web page www.airframes.co.uk/ and look under "projects" that may help.