Getting chamber inserts

Surely a zinc alloy receiver (upper and lower) are too weak to contain 9mm PAK blank ammo?

I'd be very careful attempting this, there's a good chance the chamber and receivers will fail catastrophically unless remanufactured in suitably heavy, reinforced steel.

Years ago, I made a chamber insert and new bolt for a Marushin XM177 to allow it to fire 8mm PAK blanks. The bolt and carrier was a complete scratch build, with a firing pin and plunger type spring loaded ejector. I designed the chamber and insert so it would vent out of the ejection port, with literally no modifications required on the model gun apart from removal of the original chamber and ejector. The front of the chamber was blocked so, as I said, it became a side venter.

I also 3D printed an adaptor that allowed Bruni 1911 magazines to be used. Chambered fine but the issue was the hammer spring being a light hitter. The primers on the 8mm are a lot tougher than model gun caps so require a lot more force for detonation. It would take up to three hammer strikes to actually set off a blank. It sort of worked but I became concerned about the stress on the model gun receiver so I abandoned the project.

It also wouldn't eject and chamber the next round when it did eventually fire so I'm not sure. This was before I had a phone with a slow motion video camera so I couldn't analyse what was going on.

I gave up not because of those issues but for concern regarding the strength of the system. I was paranoid about an almighty explosion occurring so decided to call it a day. There was no visible damage or cracks so it may have continued to work fine. Who knows.