In the process you have described 2-D xray is sufficient as you are looking for sufficient coverage and that you do not have large voids.  a solid connection is best, followed by small voids, then baby Swiss.  If you see large voids (you should not see this if you are using prefroms), the process is not stable.  You do need to make sure you profile to ensure that you do not have excessive heat draw and retention from the heatsink itself.