Awesome! Thanks much Nate. I purchased the wrong kit - but didn't know it. I have the Striker "generic for inverted forks".
The Trailtech website shows Gasgas up to 2016, and then 20-21. So weird - nothing for the 2018-19 XC300. I'll go check my caliper for a mounting hole - but if you say it works, it must! since I think you have the EC, and our bikes have the same calipers/brakes, etc.
Thanks for saving me from making a mistake!
Jeff