Ok I have received my rubber samples and notching tool and performed a hand-test only but I am happy with the results.
(Please disregard the fact that my cut line is not straight lol)

Now I will cut my metal-slot guide to cut an actual consistent sample. I believe this process will work out like I envisioned though.

https://i.postimg.cc/8JJrWFWB/IMG-0355.png

https://i.postimg.cc/jWjfx3S1/IMG-0356.png

https://i.postimg.cc/GBSyHPBm/IMG-0359.png

https://i.postimg.cc/phw5B2JN/IMG-0360.png