From what I understand, the 'liner' is glued in just a few spots. And what funky poodle says, there must be a reason that resonators with the liners removed never got them out back in, must be really tough!
I recently came into a 3 piece resonator in jazz sizes with liners intact and near mint but only the 14'' floor rings forever, coated remo's all the way around but the 12'' rack and the 20'' kick don't ring at all! So tempted to remove those liners to get just a nice 3 ply birch shell sound like on my other set of Premiers (Olympic)! Luckily having been around VDF for a while I don't jump into altering vintage kits, altered nothing actually on any of my vintage buys...