Since Buckshot wants to shoot heavier bullets my (admittedly unclear) suggestion of using a mostly stock Mini-30 in 7.62x39 is moot.
Since you're using an aftermarket barrel I'm assuming that yould make it a larger diameter, these pencil thin Ruger barrels heat up and start throwing 4-5 MOA patterns after a few shots. In addition to Ruger gas blocks modified to be adjustable ASI also sells thier own custom gas blocks for larger diameter barrels. I think I saw an adjustment screw on one of those at thier site.
Have you been to the Perfect Union site? Tons of good Mini info and you should be able to find a folder there. You'll find bedding how-tos, trigger work tips, etc. A couple of guys there have MOA Minis with stock barrels using inexpensive barrel struts or tensioners.
http://perfectunion.com/vb/forumdisplay.php?f=86