I have been told(by a well-traveled truck mechanic) that the trucks that came with the V-series Detroits are very poor candidates to convert to a 6 cylinder inline. It can theoretically be done, but it is nowhere near worth the time and expense. Frames/radiators/cab orientation......something is made different to cause it to be a major PITA to convert.

I suppose if you had a rolled or rusted donor of the same style it might be more do-able.