For SOF, I would love to see a darker translucent red for the ramps, similar to the red flippers and cabinet buttons available.
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As to what is under the ramp, there is the magic tunnel which leads to the upper PF, and below that, nothing. That's part of the problem with clear ramps, as the game was never meant to have some of that stuff visible.
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I can't seem to find it, but there is a website where a guy who does complete restorations did a complete overhaul on an SOF. That one definitely shows the blank PF. I'll keep looking and update if I find it.
EDIT: It was Chris Hutchins. The actual restoration gallery is private now. Finished product gallery linked below. Does anyone know his pinside username? Maybe he can post the pics we need here?
http://christopherhutchins.com/gallery/album348