Here are some pictures and an explanation.....
This is the look I wanted.


I lowered the drivers compartment by 3/8 of an inch.

I marked the areas to be cut and then used an x-acto saw.


Mark the drivers compartment and cut the 3 sides.


Once this is done, you will need to cut out the armor just behind the drivers area and add a new piece so the slope of the angle is correct.

Here it is after I cut both sides.

I cut from the inside using the sides as a guide.

Styrene Sheet and Squadron Putty can be found at most hobby shops.


I hope this helps.