Exchanging Source Code between VW5i.4 and Squeak3; Best Practice?

Hello all!

What is the best practice when I want to write one source code
for both Squeak3 and VW5i.4.  By that I mean only the source code,
ignoring differences in supplied classes by the system.  

I also want to keep source code in a CVS repository, for easy
distribution (hence it suffices, if I can occasionally generate the
source code that is to be checked in into the CVS repository).

All I tried so far turned out not to work (using Pepe2, fileout ..
filein).  Thus, I believe that I need to maintain two different versions
of the source code; one for Squeak, and one for VW...

Any better ideas?

Best regards,

Sven C. Koehler