I should have been thinking yesterday, I think it's like the 62 Oldsmobile in order for it to run it has to have its breather on and fully sealed with the air vacuum hose hooked to it to start the car
The '61'was a larger car, as was the companion Fairlane it was based on. The grille was a cat-hissing concave unit, that Dodge used in concept for Its' grilles on the '64 440 and Polara. Also, taillights were Pontiac influenced wide oval units as opposed to the Montereys in the 1961 Merc lineup. Taillights and rear valance design owe to the '59 models. Whatever; this is far and few between on the market as Mercurys go, and you just can't miss.
Mechanicals are easy; you could even go with all Mustang drivetrain and tranny. Body needs, and this car needs 'em, are as much as you don't want to hear it, something else again. But this car's worth the challenge of.