The QE barrel shouldn't make a difference. Only the end is different. The barrel needs to be unscrewed to install bullpup kits on non-qe models too.
what type of stock are you looking for? Is it a bullpup kit or just a regular stock? you could try that guy at air rifle stocks. He makes custom stocks and he seems like a good guy from my limited interaction with him.
You could also look up the Steyr Aug airsoft mod for the AT44. It's a very easy mod and it comes with a pre-installed bullpup trigger.