I've knocked the blind nuts out on ARF's then drilled the holes larger and epoxied in dowels. then just re-drill and install the blind nuts to match the new mount.

I would seriously re-consider that engine though. From what I've seen of this plane a .46 2-stroke or .70 class 4-stroke is plenty. The .91 could just end up adding more weight and being more trouble than it is worth.