Not sure what you mean by "headless " action screws.....all mine are 5/32 hex round heads ( 1/4 x 28 TPI).

I'd strip off the paint.....looks kind of flaky anyways from the pix.

Put the putty in the screw holes in the receiver.....that way when you lay it in the wet epoxy and start the action screws no epoxy can lock up the threads. If you coat the action screws with lots of release agent the epoxy won't stick to them even if some gets into the pillars.