This is the old t-shirt. I carefully cut around the skull and crossbones leaven some black around the edges. I had a plain red short sleeved shirt that currently fits him.
This is cut out and the fabric I got at Michael's that I used for the sleeves.
I used some iron-on strips (not sure of the name) and ironed it on the shirt. Then I sewed around it twice and cut off the excess black.
Using a shirt that currently fit him I used it as a template to cut sleeves and shaped them and sewed them on the red shirt.
Here he is wearing it. I actually turned out pretty good and he loves it.