You need different lens mounts. There are mounts made for this enlarger (and turret) that add about a half inch in length and eliminate the problem you are describing. You don't need to get a different enlarger, or have anything custom made. They are on the auction site frequentely. The other alternative is to replace the turret with the single slide in lens mount, and then any lens will screw in with no problem.
This pix show my turret with 3 EL nikkors - the 63mm, an 80mm and a 105mm. The 80mm is an older one and mounts on a flat board, but the 63 and the 105 require the extended "board". The pic in the middle is the single mount. It slides in just like the turret and you can put any lens/mount on it.
Hope this helps.