Yes....the bolts go into the bore, then are drilled out. Since these are salute cannon only....do you think there would be a safety issue?
Blanks work because they have pressure. Like George say debris and fouling can and will build up in the thread and start corrosion which will grow and slowly weaken the trunnion. I think if you have a failure with these guns you are more likely to sheer a trunnion off than have a blow out. But a blow out is possible. I don't think the barrel will burst but it could. Most cannon accidents we hear about is from blanks.
Go to the stickys at the top of the forum and look for the Safe loads and construction post. In there is a link to the N-SSA and their instructions on making barrel liners. Get some extruded seamless tubing, not welded seam and make barrel liners. The don't have tbe the the big heavy liners that N-SSA call for. Thin with proper breech plugs as explained in the N-SSA guidelines will work.
Bore your barrels out and glue in the liners.
Even better as small as your gun are you might be able to make you own liners from solid stock by drilling them out. This would give you a solid liner and do away with the fuss of installing a breech plug
