It is not absolutely required to index it, but I do highly advise it, partially for the reason you said. It is a simple task of drilling a single hole in the tensioner bracket. I also recommend to cut off one stop ear on the tensioner so it can be opened further, and to also make a new longer lower alternator brace. This is just a piece of 5/16" x 1" flat steel bar stock with a single hole in each end. By doing this, you will be able to set the belt length and tensioner position relationship, so it will work well regardless of what alternator or compressor clutch diameter is used, with only a single belt length. Use Vice-Grips or a C-clamp to position the alternator lower ear on the lower brace in different positions, and test fit the belt on, then relax the tensioner and see how everything looks. Adjust as necessary, drill your hole in it, then cut off the remaining lower alternator bracket length. This sounds like a lot of work but it is not at all. It goes very quickly, and allows you to setup your serpentine drive exactly how you want for tensioner position and belt length. The water pump pulley is non-flanged, so I advise to slip the belt over this pulley last since it is easiest and needs the least amount of slack to do so. I'll attach pics of the 360 degree adjustable tensioner bracket I made (3/8" steel plate, 5" x 5"), but I only used the next hole clockwise from stock location, and that can be drilled into the stock tensioner bracket, without needing to make a "revolver of holes" type bracket like I did. I wasn't sure where it would need to end up so I made it that way. Used transfer punches to copy over the original hole locations, then just eye-balled the remaining circle of holes and went to town on a drill press. Ended up not needing but one of them. Oh well. Part of development. Also notice the alternator lower bracket as a plain steel bar in fit trials with clamp and finalized with hardware and cut short. The disassembled pic is only if your tensioner bracket won't easily come off. They are 2 Allen head bolts, mine did not cooperate, so I removed the thermostat housing, drilled the heads off, removed the bracket, and the bolts remains then spun out by hand. Replacement Cummins bolts are Torx head, so, slightly better. The tensioner bracket bolts to the thermostat housing and comes off with it, so this can easily be accomplished on a work bench or vice if you also need to drill out your 2 countersunk tensioner bracket bolts. But honestly, once off with the T-stat housing, just leave the tensioner bracket attached and drill it like it is, then reassemble the entire housing onto the engine. The 10 O'clock hole is the stock position, and the 11:30 hole position I used (next one clockwise) makes it an absolute perfect fit, especially when the limiting tensioner stop ear is sliced off to allow it to open further (this ear seems to only be useful when an opposite spring is installed in this same housing to limit the hard stop point). The upper compressor bracket has oval slots in it also, so it's fore-aft position is adjustable for belt alignment. Working stock alternator which was removed during this upgrade is listed in classifieds if anybody wants a known and tested good one/spare.