Well, time to come back to this thread. . . with a 34 (not the salient arms one, sadly).
The Prime 34 kit finally arrived, all I need now is a base 17.... oh well...
Oddly enough, the BBU sits even LOWER than the guarder cast slides (tested with a 17 I already have). . . I thought prime would be a drop-in (specially with something as easy as a glock. . . ), we'll see how that goes.