I have done something like this,but I probably would not on a Phaeton.I bought a closed 30 pickup cab in 1985 and replaced the coupe body on my 30.Then,in 2008 one of the previous owners started making sounds about wanting his cab back.He is a friend I went to school with and his grandfather had given him the truck.His dad was kind of an ornery cuss and one day in 1970 the guy came home from school and the truck was gone.His dad said you don't need that old junk around.In 2008 I was also driving a 28 roadster pickup,but I mentioned I would like the 30 style.He offered to trade me a new open cab for my closed cab.So we swapped,while I was at it I put a better frame under it,higher gears,repoured the poorly poured rear main,went to cast drums,better fenders and wheels,new bed,now I am putting together another cab on the old parts I had left over.We are non-title here after 15 years,we can change a body style by just telling the town clerk when we register.If we want to change a body style in the middle of our registration year,(if we even bother)we go to the town clerk and she makes a change with a pen,then initials it.It will get officially changed at the renewal time.Costs a total of $12.per year to register an antique here.