Paul; You mentioned perlite. We have had a couple of members, who have experimented, successfully, with “ceramic wool”. Don Mannes has used regular WK design (sort of) with steel tube and one with ceramic wool; plus a build on charcoal, so pay attention to which build you look up.
The other build was the initial build with ceramic wool. Look up these two. Firebrick gasifier (modified WK), 94 Dakota and Featured Project _ Dustin Moore’s Firebrick Gasifier TomC