Painting the Premier DHC6, how to make lines along the plane?

So I'm just getting into painting planes and I've done a custom paint scheme on the TDS 787-9 and the PAD ER190. Now I've set my eyes on the PAD DHC6 Twin Otter. This plane has a special place in my heart as it's the plane I jumped out of in my youth. I'm having a hard time with their paint kit for it though. I want to do a design that runs along the entire length of the bottom of the plane, but the template has the kit split in 2 and no reference lines showing how they match up. There are 2 faint lines that appear to run the length, but even they don't line up if I try to paste them together in PS. Does anyone have any ideas?