Nice going. If you do something more permanent, maybe a 3D printed adapter, please post.
I hacked my V Hasselblad folding finder by removing the glass loupe plate and inserting a flat Fresnel reading lens that I bought in some mall. For me this was a big improvement. You might find this idea useful. I think there are also some super-luminous focus screens around somewhere.
Back in the days when, I asked the Hassy CEO why they didn't have an H vertical finder, and he said no money. I think they did the cheapest design they could and never revisited the issue.
Edmund