Headlamp mount install help

my 95 Mystique took on a deer last week taking out the passenger side headlamp assembly and the mount behind it(which extends across to the driver side). I got a headlight assembly/mount with headlight reflectors mounted in it, but need to know what is needed to correctly install it. I cannot get the assembly to fit in the quarter panel opening easily and do not know the correct procedure to install. Any hints??