Ok so I measured the pan and it would take some fab work to make it work.
The trunk pan from this Newport is about 6" longer(deeper)
The hump is slightly different going over the axle but it looks like it is the same width with a different sweep angle coming off the hump into the trunk as well as where is attaches to the wheel wells This could prove problematic attaching the truk pan to the wheel wells.
The biggest difference I can see as well is the two cut areas where on the Newport there are the mounts for the rear bumper.
The Polara has thin brackets coming up from under the base of the trunk whereas the Newport has the major wide brackets coming of the back plate of the trunk into the trunk.
These brackets are about 18" wide and go down on a angle into the trunk about 6"
If you are looking to simply cut the bottom of the floor and not try to go up to the hump then you will need to only modify the rear of the pan but since it is longer by abut 6" you can cut it shorter
this could also affectthe mounting position of the gas tank too but you would have to use your original brackets or if they are rusted too badly use the ones off the donor parts I have.
View attachment 102550 View attachment 102551 View attachment 102552