In the end, it'll probably not matter all that much. I'm sure it's less brain-shattering for Burger if you just didn't turn things into fancy mechanics. It's easy enough just to have injuries pop up on Kori while someone else takes less damage than they expect.

That being said, neither STR nor END really contribute to the ability for people to block blades with their muscles, because even GARETH LANDROCK, STRONGEST DWARF OF THE DUNGEON CITY, gets his butt skewered constantly. So even if Kori and Grim stacked their stuff together, it'd be more like 'stabbing through flesh that is 2x more dense' rather than 'stabbing through defensive values of D+ x2'.

END's more like stamina, afaik.