I would like to make a simple ViewMaster, but for 6x7 film instead of those little postage-stamps on a wheel. I figure this thing will be to projection as headphones are to good speakers In other words, I'm trying to build viewfinder optics; something to make a view-filling image from a frame.

What sort of closeup lens do I need so that the user's eye can focus on the chrome while filling their vision? How many dioptres do I need for typical vision? Would it be reasonable to use a pair of closeup dioptre/filters intended for use on camera objective lenses and can I assume they'll have good enough FOV on an eyeball and sharpness across the frame? Do I need any optics other than a closeup filter?

No I'm not going to use two RB67 prisms! I want this to be usable by people other than weightlifters, not to mention people with an inter-pupillary distance smaller than an elephant.