Heard back from Ruger today, here's their response;
"The AR-Style magazine well conversion kits are sold through customer service for $19.95 plus $6.00 shipping and handling. Please be advised, we have not tested this model with the AR Style conversion and cannot guarantee that this will be compatible with your firearm, however the AR Style conversion will accept any AR style magazine. If you decide to purchase this conversion kit, there are no returns or refunds on this kit. We also do not offer the AR Style magazines for the 7.62x39 and the magazines would need to be purchased after market.
You may reach us at 336-949-5200, option 3 and option 1 (Monday-Friday 8:00am-5:00pm EST) and provide the serial # to your firearm to place an order."
Hodgie, have you actually done this(or anyone else for that matter)?
I do have a Ruger American Predator in .223 that is the AR style mag setup, so I can swap the mag-well adapters over between it and my SIL's Ranch, borrow(or buy) a mag in x39 to test and confirm if need be.