up to this point, any _factory_ Crosman gun that had the pistol grip could only be made into a "rifle" or carbine by adding the 1399 carbine stock. Reason for this is the pistol grip.
The pistol grip works great for _pistols_, but pushing that format on out to the carbine concept and you'll find some issues quickly. IMNSHO, you really only have 4 options to correct some of the issues on the 13xx/22xx guns: 1) use the carbine setup "as is" 2) mod the carbine stock to correct its own set of sortcomings 3) buy one of the offerings from Chavka/Corcaran et al (simply bolts on like the 1399 stock, but is wood and corrects much of the plastic stocks short comings) 4) lose the pistol grip altogether and swap on a 2260/disco/marauder trgger pack and go with a more trdtional (and mostly custom ) stock offering . Notice I didnt mention altering/modifying the factory pistol grip frame. I ignore that choice becuase you dont gain much ergonomically, as the trigger is still close to the middle of the pump tube and _that_ is what confounds the ergonomics (Now, Andy's frame mod trigger setup corrects that, but we are back to custom work)
AirGun Nirvana's way cool build shows what _could have been_ from our beloved vendor. In that case though, I think the stock will be what keeps that from ever being a Crosman product. They have very thing else already in house. Even if they went synthetic, there would still a product development cycle (and all that entails), market trials and getting the variuous retailers to carry it. The real question is whether the shoppers of Walmart et al are going to accept the level of performance from that platform at that price point (and I do think it would have to be somewhat higher than just the 1377 clamshell retail pack) when there is already a 1377 based gun that has a stock and will cost less than what the "1377S" would retail for: the 760. (Yes very much aware of the differences, but the general public may not be, nor care, given the dollars involved.
I'd have to guess that AGN's build would appeal to a broader spectrum of shooters, especailly if they have powder burner bacground. But that's where I have to take the othe fork in trail, and say you will need a synthetic stock, in a pistol grip (not grip frame, think AR-15 ) or synthetic stock--black, of course . Then it will not look like anything else on the shelves, and you could hawk it as having </boots on>"features that enhance ease of shooting and accuracy,,,,,,"</boots off>
hehe I dont see that happneing either, so I think its on us, the pumper fanatical, to push this forward. Andy finishes his build, AGN already has one, Ive got a 1377 side pumper build on the bench (but on hold till after the Nats). And No Rob, I'm not advocating another 1377 build off. 
Thoughts?
dr_subsonic's pneumatic research lab
the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic