Anti burst lock barrel

Hi all. First posted this on the Defender forum - plenty of reads but no answers. Locks are same as series LR's so can anyone help?
Vehicle is 1994 ex-mod defender with military style doors and anti burst locks.
About to fit new a new lock to off-side front but want to refit the existing lock barrel.
I've only done this type of thing, once before (on a different landy) and I can't remember how I tackled changing the barrel over.
Advice welcomed.
Rgds

Take a photo of the door handle & barrel.

Think there is a hole you poke a rivit down to release the barrel

Cheers mate,
Job done. Used an old 2mm dia twist drill just to push the barrel release button down - once I'd managed to line up the hole in the lock body and the release button. Bit tricky getting barrel out with liberal doses of WD 40 - been in there all but 30 years.

Rgds