I just installed a Bosch rebuilt Alternator on a w123 with single pulleys,the recommended belt from my dealer was the 13 x 1030,i had to take it all apparft for after a short ride the front plate on the pulley was dissentegrated and the chuck key had moved out of place on the pulley groove where it should fit.
My questions are is that chuck key supposed to be aligned in that grrove all the way to the top while i tighten the bolt,i cant seem to be able to do that very well with the impact wrench i need to use to tighten it,the thread is a little bad on top and i need air to get it in place but im not sure about the chuck key yet,another question is do you guys think i'll need a x1050 belt? alternator goes in nice and so does belt,i just removed pivot bolt and put belt in before i tightened the alternator up.
Thanking you guys in advance

Just use a belt that allows you to (1) get it on the pulley and (2) is short enough so that you have at least 1" or so of tightening ability after it's on. You may have to "bump" the belt on (putting it on the crankshaft pulley (the innermost one) and the alternator and then as far onto the fan pulley as you can get it from the alternator side--then just touching the starter. Most times it will pop on, and then you just tighten the alternator adjustment nut, and afterward, the other bolts that allow it to pivot (and tighten).

I found that the parts store was more than willing to install the pulley and woodruff key on the rebuilt alternator. They do it all the time, and takes about 3 minutes.

Good luck!

john bonds
Carolina: '82 240D 4sp 200k

Got it this timew,the bracket had bent and i had installed the previous one kinda sideways making the belt eat up the front of the pulley,this time i used new pulley,belt and bracket,im good thanks crew.