Using the Buick floor and chassis made this part of the project easy. The front crossmember only needed to have the engine mounts unbolted and the Chevy small block mounts from a 80's Caprice bolted in. I am building a mild 327 with a 200r transmission, so I fabricated a cross member for this engine trans combo. The front and rear frame horns needed to be trimmed slightly and I modified them for the new bumper mounts. The biggest modification that I made was removing the weak factory 7.25" differential and adapting a 1970 12 bolt. The 70 diff also has the advantage of being nearly 1" narrower, allowing me to run the wheel and tire combo that I wanted.
I was able to retain the original wheel wells from the Mercury as the floor from the Buick slid right between them. Once everything was welded up and cleaned it was time for paint and undercoating. I live in a rural area and this car is going to get driven. LOTS!
With the newer chassis under the 4.5" channeled Merc body I needed to change the rad cradle and inner fenders. I made up a new cradle to fit past the Buick steering box and made inner inner fenders that work with the control arms. A new Griffin aluminum rad will take over the cooling chores.