Acetone will not affect polyester the same as acrylic. I would suggest avoiding this unless you have quite a bit of experience with the resin and by your questions I don't know that you do.
In my experience polyester is more susceptible to bubbling than acrylic, not by much but I have noticed a trend.
If you have a vacuum pump with filter and have quite a bit of experience I would have suggested molding the scales with the original inlays in place then fix the inlays in the mold and and cast the scales around the inlays fixing them in place, then vacuum the bubbles out. this can be a pain with no previous knowledge of this method.
There was a thread on here giving details about moving inlays over, I think it was Glen, but I cannot find it in my subscriptions right now. You may want to search for it.
As for the polyester, I would cast the blanks larger and cut the scales from a larger blank.