Congratulations on your purchase. I have three of these enlargers and I am sure that you will be happy with yours.
Durst makes two enlargers in that series...the 138 and the 138 S. The difference is the assist on the table with the 138S.
Durst has two turrets for these enlargers the Unipla (single lens) and the Tripla (triple lens). Each of these turrets takes different lens mounts which are specific for a given focal length and manufacture of lens. If you could provide me with the lens manufacturer and focal length of the lens(s) that you intend to use then I can give you the Latub designation(s) that you need for your enlarger (at least what Durst shows in their manual). I just looked in the manual and there are forty one different designations that are dependent on the turret, the negative size, the lens and the lens manufacturer. The Latub could probably be machined (no doubt) but the machining set up would probably be expensive since these are turned on a taper.
Message me if you want me to determine this for you. Good luck and enjoy.