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Ted --
Yes, it's possible to sandwich your step tablet and film in a printing frame for testing, in fact that's the preferred way to go. Providing a workable light source will be your main problem. First, you'll need an electronic timer to provide consistent exposure times of no more than 1/2-second or so. Then you'll have to cobble up a switchable light source that can provide uniform intensity on your work surface at a maximum brightness of EV 4, more or less, as measured on a white card with a spotmeter (set on ISO 100).
This is a very low brightness level so you'll have to reduce the light intensity somehow. One possible way to do this is to use a small light bulb in a reflector directed away from your work surface—on the opposite side of a large, otherwise dark room, for example. Covering the light with paper will probably shift the color toward yellow (not a good idea) but you may be able to find some screen material, such as fiberglas cloth, that can reduce intensity without affecting the color.
When you've managed to get uniform EV 4 illumination on your work surface and your light switches on and off consistently at 1/2-second, you're ready to begin testing 100 ISO film. Adjust the illumination to EV 2 for ISO 400 film, EV 3 for ISO 200 film, etc. No doubt some adjustments will be necessary. Good luck!
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