Well, it's already been done, and I'm happy with the results.
There was an attempt to use the old spindle,
and on a loose fit it appeared to work.
But when it was tighten down, it showed itself to be to short.

I think I could tell the wider Q-factor, but it might've been in my head.
Anyway I've already adjusted to it.

Plus along with my 52/40/32 combo,
I have extra rings in 53,46,42,34,28,
I can try mix and matching, to get it down to where
it fits best for my riding.

Although the shop was leery if the 28 tooth,
could be used without more modifications.

The owner of my LBS, was at one time long ago,
the local dealer for French bikes.
So he likes vintage French bikes, if only for nostalgia.
Going as far as when the vintage bikes come in for repairs,
instead of hanging them up on racks in the back,
he puts them out on the floor so people can admire them.

So I tend to trust him and his techs.

Except he was putting pressure on me to upgrade to a TA crankset.