BB spindle length

I pulled my cup and cone bottom bracket apart yesterday. It had been
exhibiting some play, but not not evenly throughout the stroke (more
play at certain points, little or no play at others). The spindle had
a small amount of pitting when I last put it together. I had plans to
replace the whole works eventually, but this time loose balls fell out
of the cage on drive side, the spindle and cup was chewed up pretty
badly halfway around.

The spindle was a nondescript looking thing (probably original on this
'86 Trek 400) - seems to be about 118 mm long overall (with studs
beyond that for crank arm nuts). Looking through available spare
parts, I came up with 113 and 122.5 mm spindles. Compared to the 118,
the 122 extended a bit longer on each end. The 113 was mostly shorter
on the drive side. I also came up with plenty of good usable cups and
bearings.

I've been needing to replace the left crank arm anyway, so I ordered a
pair of crank arms (Shimano FC-1055) that are supposed to work with
the 113 mm BB.

Meanwhile, I installed the 122, put everything back together.
Everything seems to line up okay. I didn't even adjust the front
derailer, and it still seems to shift okay and no rubbing anywhere.

I guess the one thing I'm worried about is possibly overshifting past
the small ring, which might conceivably jam the chain between BB and
crank. My plan is to just be careful and see how it goes.
(Fortunately I usually only downshift the fder once on my way to work,
and then once more just before parking the bike.)

I expect that I'll have to move the fder in for the 113 mm spindle and
new cranks.