Bedding rail to Mack Bros Element action

[Halleywood]

I am looking to bed a one piece picatanny rail to a Mack Bros Element action and when I took off the 2 piece base of there is a rectangle cutout on the back of the action. It's missing a good chunck of the space the epoxy would bond to. I'm curious what you experts would do? Just epoxy it as is? Fill it in somehow? Something else?
Thanks

 

[BBob]

Epoxy to what is there, ignore the hole and call it day.