[aerohead]

At GOOGLE IMAGES there is a photo of a Beetle in VW's modern tunnel with smoke being blown over it.I think it's in 'WINDKANAL' as a search title.
Anyway,the forebody looks okay,it's only at the top of the backlight that she 'loses it'.
As with the Airflow,I think the Bug would respond favorably to the tail even if you were to do nothing at the front.
I would work on the sides.All that you can stomach.
But (yeah my English teacher would spank me) it would be better to do a truncated tail of proper design,rather than a 'full tail' of improper design.
I just posted a thread with W.A.Mair's boat-tailing.You might want to give it a look.