Can I bolt a 1600 tp straight up to a 1200 gearbox in my 63 beetle??

No

a 1600 is a 12V and you will need to change your flywheel
Depends on what gear box you are running as well

Standard 1200 gearbox that came out in 1963 beetle!!

then you can clearance the bell housing but it will rev its tits off

GREAT for the traffic lights

RUBBISH on the highway

This question gets asked all the time.

I have a 66 beetle with a 6v gearbox. I ran a 1776 12v engine, and all i had to do was grind out the bell housing using emery flapper wheels on the drill...
I converted the whole car to 12v at the same time.

Here is the thread i started:
http://forums.aussieveedubbers.com/viewtopic.php?tid=106941 

Here is my members ride - look about half way down the 1st page
http://forums.aussieveedubbers.com/viewtopic.php?tid=106947