Cheers for this info - it answers the main question I was worried about. I had tried some nylon spacers in there for testing, and ended up with 1/4" thick in the rear and 3/8" in the front. As you suggested, this gives just enough clearance overhead at the rear of the sharps, and just enough clearance underneath between the naturals and the front rail. But it results in the keys being slightly tilted, i.e. noticeably higher at the front.
...But it sounds like that's normal for a Mini. (I've never owned one, so I'm kind of working blindfolded here!) It seemed wrong to me at first, since I'm more used to working on organs and pianos, where the keys are flat level front-to-back. But after reading your post I looked around at a bunch of pics, and it looks pretty clear that Minis were just built that way for some reason. (Anyone know why?)
Anyway thanks again... this thing is coming together slowly. All I had to begin with was an empty cabinet, nothing else -- not even a bottom panel. So this kind of info is a big help to me.
---In vintagesynthrepair@yahoogroups.com, <winking_n_nodding@...> wrote :
The sims, I recall are fiber board, but metal would work, as long as you glue down for ease of assembly. You want the back of the key to not clank against the case as the key travel up when released, yet have a minimum gap. The front sims are thicker, so that at key down, the key is level. Piano thing, personal thing, otherwise it could be level at key up, just don't want the key to bang at key down either.