I was just looking at the engagement on both the M70 and a MAK 90. I thought more of the lugs' surface area were in contact than that. That is a pretty small amount of area in contact.
I may go back to my original plan of making my own bolt/trunnion. Still a two lug design, but much larger lugs and surface area in contact.
The main loads I was looking at were 90 gr bullets and lower charges, but I'd like the option of much heavier loads. That of course would require the custom beefy design.
I'll post some schematics of the original design ideas this weekend.