Just found a L67 engine out of a 1999 Park Avenue Ultra with 51k miles on it for $500 in Remington, VA. It is missing the Supercharger, but to use it on a 1996 car would require some vacuum line modification, so it'* best to retain your original supercharger. I'd suggest stopping at your local dealer at the time of the swap and getting 2 $7 bottles of Supercharger oil and changing that (allen head screw on front of SC nosedrive).
The SC gasket can be bought at Auto Value or anywhere that sells FELPRO brand gaskets, and the SC gasket for UNDER $16 (Felpro gasket comes with coolant o-rings and the GM gasket doesn't so the dealer charges something like $30 for the gasket and 2 o-rings).
Stock #: 607853
Part Grade: A
Remington Auto Parts