>   I think the way Westfalia did those pre-74 pop-top openings was to use a 
>   sunroof body, without the sunroof. My '72 Westfalia <with forward hinged
>   pop-top> had a "double-roof" behind the opening which formed a cavity like
>   the one that a sunroof would be withdrawn into. It was a good place to carry
>   skis, by the way.
> 
>   Soooo, if your present bus has a sunroof, you could go ahead with the 
>   conversion to pop-top.
Indeed you can, but really, I would say it's not that bad cutting a hole
out for the top. My '78 had a sunroof, and I mounted a '70 top pretty
easily; it took about a day, with a friend helping. A friend of mine did
cut a hole in his roof to install a top, and it wasn't a problem. He put
on a non-westy top though...but it's a good day or two project.
I recommend it, and think it would be worth it.
Richard