I have done what your asking about - It is a lot of work and a lot of money to do it properly. For the street it is way overkill, for a race bike that is a different story.
I have a 70mm bore in a 650 block but it runs pretty hot and I would not recommend it. Those 70mm pistons are custom, piston manufactures stopped making that bore size 30 years ago, then never went bigger than that off the shelf.
You just can't stick 1000 pistons in there, they have 17mm wrist pins, the 650 has 15mm pins. The 750 turbo has the rod ends at 16mm, but I think that is the safe limit for those rods as far as the small end goes, opening them up 1mm might not sound like much but they were never designed for that. You don't want to mess with the rods, that is the weak link and for sure may spell disaster for the motor build if you mention cutting/welding its just not done.
It may be possible to go to 73mm but I don't think you could do it with the 750 block as it would be very thin. Using the 650 block it is impossible as the liner is outside the casting front and back. The only time I have heard mention of a 904cc motor it had a billet block, look over on the UK 750 Turbo forum.
Just stick with the 69mm Wiseco 810cc kit for the 750, it is much cheaper and easier to do, virtually no difference in performance from bigger bore sizes.
On these smaller engines the limiting factor is the small capacity, your not gaining much HP going up 810 to 904cc. The cost far outweighs the HP increase, more power per dollar spent can be had with a better cylinder head/cams/carbs.