If you can locate a focusing hood that fits your model, you can remove the upper moving parts. A Haaslebad finder then fits in the opening. You need to put spacers inside the finder to raise the Hassy part up about 5mm to get it to focus on the Rollei screen (still in place and part of the hood base).
Be aware that the hoods changed a bit for various so check screw location and front and back point locations before destroying a hood from a model different than yours.
You can put the prism inside the hood base and tape the crap out of it to hold in place. Works fine.