Trial and error with cardboard is probably your best bet. Even with someone else's dimensions/measurements, there will be some trimming to get it right.
Ahh the school of hard knocks,.........those were the days....
The place where everybody told you NOT to put black pinstripe tape on every body line your 69 Mach 1 had, but you did it anyway. The same school where they said that a 10' long CB whip antenna would look like ass bolted to the quarter of the same car.
Some people just have to go there Noobz, it'll be the only way they'll ever graduate.
I was 17 when I said to myself "Let me strip out my perfectly good A/C system on my car to make it 30 lbs lighter because "RACECAR". That one move cost me years of regret and nearly $1K in NOS Ford A/C components and R12 to put it back in the car (which I still haven't done).