I have Pachmayer swivels on a Martini, and a Hogue stock on a Vanguard,and I don't think the two are very compatible. Maybe if your stock is the full bedding block, mine is not. With the pillar bedded model,there isn't much to sink the threads of the base into. The factory uses a thicker section of plastic and a metal washer to anchor the front base.I suppose your best bet would be to reinforce a section in the desired location with epoxy and maybe a metal washer,or a small aluminum block threaded for the Pachmayer base. The flush mount bases are considerably bigger in diameter than standard bases,and aren't long enough to thread a nut onto. I suppose it's doable with the Hogue, but won't be real easy. As far as the base on the butt, maybe pull the pad off and see if you can do the same type of reinforcement back there,of leave the original in place. Drilling through the rubber overlayer may be tricky too,maybe use an Xacto knife to cut the rubber before drilling the underlying plastic to keep the dril bit from grabbing and pulling the rubber.Just my two cents.
