That pla is going to burn out like a champ I think. Fingers crossed it doesnt expand like wax and bust your shell. Take your time between coats. Last coat is slurry only, no sand.
I put one part that was printed heavy walled and fill to see how the shell handled it. I looked in the kiln when it was at 1500F and I did not see any cracks, but it is difficult to see much when your eyeballs are burning up. Ill pull the shell tomorrow and inspect, looks promising so far
That's a really thick shell. Let's see what happens when you play by the rules this first go. Maybe you can thin it down later and save some time and money. FILM the pour and breakout if you can please.