How to carve an irregular opening - Senior 20 Organ

How to carve an irregular opening Senior 20 Organ

I am not sure how exactly to post here, but here is the problem.
I am trying to make the front for a crank organ.
Look up
“Busker Senior 20” online. For pictures.
I posted a Cut Layout under the title
“senior 20 front - all corners 16 in square 15 in image edge with opening”
I would like the ability to draw other shapes such as a trapeziod.
Any ideas?
Thanks
Martin