Well after mentioning that i realized that this is based on q2 engine instead of q1 engine (and released 1 year after q2 so its probably enhanced q2 engine).

I think 770 gets around 7fps in q1 so probably half that for q2+hexen2

So i wouldnt get hopes up but i could still do a build if you want.

Hexen 1 is based on doom engine which you definately have power for, so that might be the best solution to 770 hexen. I might look into that too.