If your liner doesn't reach the muzzle it's generally not that big of deal. You just gotta be mindful if you mag dump. It's the breech side that matters more. Before you glue anything I'd go ahead and swap your printed trunnion into the front of your CMMG bolt carrier this allows you to dry fit everything before gluing. Besides nothing's more annoying than breaking the trunnion whilst joining it to the BCG assembly when the liners already glued into it . This also allows you to finalize your extractor notch you'll be filing into the liner.

This is all from memory of my build shortly after the sten variant was released so if I'm talking nonsense just ignore it.

I've still got the white powder coated right side charging non slappy style metal cover. You pay the shipping you can have it... Assuming you have a PO box or alternate address to obfuscate your identity