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There's a simple reason that all binoculars bigger than about 50 mm aperture use some variant of the "old-fashioned" Porro prisms, rather than the more compact "straight through" roof prism design - it is necessary to have a "bent" light path to get the eyepieces closer together than the diameter of the objectives and housings.
Not wanting to rain on your parade - but why not buy a pair of astro-binoculars (15x70, 20x80 or similar)?
Or fit a bino-viewer onto a single refractor OTA, if you want the ability to vary the magnification?
It seems to me that either of these options would be a simpler means of achieving large-aperture binocular viewing.
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