recompiling deb to 64 bit

[Kenneth Johansson]

I managed to confuse myself trying to recompile a few libs to 64 bit 
version doing

apt-get source -b <package> works very bad with anything tat installs 
libraries as the resulting deb installs the new 64 bit lib over the 32 
bit version.

what is the proper sequence to get it to install in the lib64 directory 
??