A conversion neck is one that can convert an instrument from one scale length to another with no other modification. A common conversion is 34" to 32". By overhanging the 20th fret, or leaving it off, you can use the stock bridge location on the body, just adjust for intonation. Such a neck will work on any standard bass body. A conversion from 34" to 30" requires overhanging two frets, or losing one or both.
The glue is all dry, time to flatten out the blank. I clamped a piece of scrap wood at the edge of the bench for a stop, and laid the blank up to it on some padding. This will stop it from shooting off when the belt sander hits it. I sorted through all the vacuum cleaner parts I have collected over the years, and finally made an adapter to hook the sander to the little shopvac under the bench. Then I put on a new 80-grit belt, and went at it.