Adam,
It is very doable, and M&G can furnish you with the needed parts. Some toads require extra needed changes like moving a battery or fuse box to gain enough room for the M&G cylinder. Just talk to the people at M&G, they will walk you through the installation.
One other thing is that your 98 Marquis may already have the air brake line factory installed for the M&G brake. My 2000 Marquis had the air line installed and plugged beside the receiver.
Gerald