Havoc, OP, do you want to futz around with gear trying to make it and then trying to make it work well enough or do you want to take pictures? At today's prices for used equipment, buying is more economical and faster than making. But if you like tinkering, go to it.
OP, some 4x5 Crown and Speed Graphics have Kalart rangefinders. These work with only one focal length, changing focal length requires adjusting the RF. A Kalart can be adjusted for a 105 mm lens. If you want to tinker, by all means tinker. But if you want to take pictures buy a Graphic.
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