Your best bet is to do it as a form 1 and then send it off to be cut down and threaded after approval. Total turn around will be shorter than going the form 4 route. The barrel needs to be cut, crowned, and threaded and the gas port is going to have to be opened some.
Contact Morgan - dallasshootingsupplies on this forum
Oak Point, TX 75068
$20 firearm transfers ($15 with CHL/LTC)
$50 NFA transfers
Find us on Facebook @HBGuns
Find us online at HBGuns.net