Middle stripe width on 2 tone paint

[CDN Sharky]

Hello I tried this in bodywork tread but so far no luck. I am doing a 2 tone paint job on my 78 gmc shorty with all the chrome trim all new pieces so I have no old lines on where the side was before. I am painting all parts seperataly and I don't want to have to put molding on to mark it if I don't have to does anybody have measurements on where the center colour should sit I know I can use the rib body line but no clue where the bottom should be. Please help