I haven't had to repair my 77/44 yet, but I did a similar repair by using a countersink bit on the inside of a stock to create an epoxy "wedge". The shape resists pull-out, rather than relying on the epoxy bond to the stock.
It helps to use a fairly high quality epoxy, such as Marine-Tex. I believe these are filled epoxies, not just a 2-part glue. They can be drilled and tapped after curing and are amazingly strong.
However, you are correct in stating that epoxies don't stick to plastics very well.