things like this are difficult to discuss with just writing but I'll try.
You just have to keep in mind the goal: getting the middle chainring lined
up with the middle of your cassette.
There are 2 shimano standards for tapered cranks, in perspective of the offset, but the
'other' standard you normally only see on the cheap bolted together cranks.
As far as BB's being compatible with your frame, there are three standards:
68mm, 73mm and 100mm, but if you have the wrong one you can spot this
easily as the cranks are not centered.
But wait a minute now I read 856, as in 1996? with as standard an XTR
BB, that would mean the splined one? Then your problem is pretty clear:
The early splined XTR, DA and ultegra BB's are NOT compatible with the
later version from XT,LX and Deore. I keep forgetting what way around
but either you had to use a lot of force getting them on either there is
some play right now. But this also explains the offset, compare the pictures:
Looks like you need either a new BB or a set of old XTR 950's Cranks
but don't keep on riding like this it will destroy your cranks