Hmm. Normally these old design boxes do have much more free play in them than a modern equivalent, but that one does sound slightly more than "normal" if I remember.
In our old vehicles, that 1.5" is not excessive, but perhaps you can still get rid of some of that in a rebuilt box.
I would not just go willy nilly tightening up the top preload screw until you talk to someone at BC though. I don't know if they rebuild their own or send them out to a rebuilder as most do, but while it's rare, it's not unheard of for even the pros to miss one in the adjustment phase.
I've seen them loose from companies like PSC and West Texas Off-Road before (mentioned here by other members) so apparently it still comes down to the humans that do the job. In at least some of those cases, putting an extra tiny twist on the preload ajuster fixed the issue. In most cases though, that does not fix it and you can actually do long-term harm if you go too far.
Hence my recommendation to wait to hear from others first.
Maybe others will chime in on the play you have and correct me if I'm wrong. If you can get an actual measurement too, that would be helpful. Unless that was what you were giving, rather than an estimate? Just to be sure since these things really are never going to be like a modern rack-and-pinion setup I don't think.
Good luck.
Paul
