I wonder where the 50k has been spent?
The spec doesn't seem anything to write home about? I'd put £50 on you taking that to a specialist to get prepared properly would cost you ££££'s.
Even the pics show a corroded looking rear underside, might only be external components but it doesn't smell great for the effort thats gone into the rest of the car.
I've re-read your post to try an understand your points.
So you think it requires more work because it's under-prepared and you can't see where the money already spent has gone?
Well it's had some shell strengthening, roll-hoop, harnesses and seats, good suspension (Bilstein) bigger rad, bigger engine, stronger gearbox, bigger diff and LSD, bigger wheels/tyres, 4 pot front brakes, underbody protection, upgraded electrics, navigator aids and we don't know the full spec. That's a decent start tbh.
I have no interest in the car but 'on the face of it' it seems ok but I've not seen it or driven it.