I got the Gravelking SKs and did some experimenting. It fits a 35mm at the back, but with only a few mm each side of the chain stays (on 20mm internal rims the come up around 36mm).
I want to go off road so I ended up going 32mm rear and 35mm front, giving a bit more clearance.
Thanks for the update. I read 43mm between the chainstays so maybe a touch more clearance with the slick gravel king and on a 19mm rim. Think I’ll give it a go.
What rims are you running btw? They look smart without logos etc
Let me know how you get on. I am looking at 35c gravelking slicks on my strael frameset when it comes