A pair of Falkirk 6 pounders c1800 with original carriages used by the Reed shipping line plying the South China Seas out of Cardiff.
Spiked c1914 when it became too dangerous and the cannon were moved to a tourist attraction schooner parked at Newquay.
It looks like the touch holes were plugged from the inside and then a steel cup was driven in to the bottom of the bore so you can't knock it out. A professional spiking, they knew what they were doing.
I sparked out one touch hole to bore depth, tried injecting rust remover but it wouldn't go in. Tried injecting 90 bar hydraulic oil and it laughed at me. Even tried a a little powder but it was not impressed.
I have a length of 1" studding which could probably pull it, but how to attach it to the spike? I don't want to make things worse so glue seems like a really bad idea. An expanding plug maybe, but I don't want to clinch it even tighter.
Bores are around 3.6" diameter by 43" deep. The cannon weigh close to half a ton each which doesn't help.
Help
Edit: Best to mention this is totally legal, I have shotgun/firearm/gunpowder permits. The cannon are pre-1939 and classed as curiosity or ornament.