I'll join the same club that has alternator belt problems. The '84 SD calls for a 1000 mm belt with the smaller water pump pulley. However, it's virtually impossible to get it installed or removed for the same reasons as mentioned. All alternator bolts are loose and the unit cannot move further inboard toward the engine.

So, what I did to use the brand new belts was to remove the fan and it's pulley........install the alternator belts in the V-groove.........and reinstall pulley. There's plenty of slack to do this..........you simply can't get the V-belts installed after it's bolted up. The time to accomplish is about 15 minutes or so...........struggling with the existing setup took hours without success.