LA Pan with MAG gasket...NO WAY.
It's on. Have a car pan as well. The car pan IS different. It's flat vs dimpled.
I suspect that your "car" pan is actually a 318/340 pan. There is no difference between truck and car pans in regards to the rear area of the pan, BUT there is a great deal of difference between a 318/340 pan and a 360/Magnum pan in that area.
If the front and rear of your "car" pan are the same, it a 318/340 pan. If the front and rear are different and the diameter is significantly smaller at the rear, it's a 360/Magnum pan, and should have a rolled bead to compress the gasket.
You should see a picture of the two pans side by side
here. (My work block the link of the picture, hopefully you can see it)
Just to be clear all 318/340's use the same pan and gasket set while all 360's and all Magnums use a different pan and gasket set.
In the end, glad you got the pan on.