Is it really driving OK mate...? It bloody shouldn't be!
What's happened is that whoever fitted the gas system secured the injection nozzles into the holes they drilled in the inlet manifold with their teeth, with small nuts bolted from the INSIDE and didn't loc-tite them - 2x nuts had come adrift and damaged inlet valves.
I just feel sorry for ya matey, such rediculous bad luck!
If she really is driving ok then worth doing a compression test and seeing if she'll continue but it ran pretty bad and was chuffing into the inlet manifold when u left me buddy