Does anyone know what modifications, if any, might be involved in installing a pair of 560sl seats in a 450sl?

 

After some trial and error, I can now answer my own question.

Yes, 560sl seats will fit into a 450sl with only a simple modification--no drilling or welding. The frame rails will need to be used from a 450 since they bolt differently into the floor tub. However all this amounts to is sliding the older rails onto the newer seat. Also, the seat belt uses a different buckle so either the entire 560 belt hardware needs to be swapped or the buckle from the 450 needs to be bolted onto the inside of the seat frame.