It's tough but you just have to work at it and eventually you'll get the
angle right and it'll just slide into place. Don't force it too hard as you
can crack the plastic. I've found that on 240's it's virtually impossible to
get it in without removing the alternator, but 740's are quite a bit easier.

It's been a while, but IIRC I tied thread to the braided wires on the
brushes and pulled them back while putting the regulator on, then broke the
threads off.

Mike

Here's how I got the regulator/brush assembly seated.  I noticed the
original assembly had small holes in the bottom of the outside housing
walls and there was a small channel in the housing partition that keeps
the two brushes separated.  It was evident that the brushes could be
pushed all the way into the housing and some straight, fine, stiff wire
could hold them in place by passing through the two holes and the
channel.  Once the assembly was seated the wire could be withdrawn.
Unfortunately my replacement part didn't have the holes or channel but I
used the same general idea.  I drilled a 1/16" hole through the bottom
of the wall at the end of the housing that extends deepest into the
alternator.  Then I unfolded a paper clip and made a small hook in one
end that could catch in the hole while the long length of the clip wire
was pressed against the bottom of the housing holding the brushes up in
the housing.  Once the assembly was seated I pushed the wire forward
enough for the hook to clear, twisted, and then was able to pull it out.

Neither assembly allowed me to see any of the braided wire so the idea
of tying thread to those wires was not possible.  As for trying to tilt
and slide, I wasn't successful and each time the brushes got a little
more nicked.  My first impression is that the alternator is OK but I'll
need to determine that over the next couple of days.

Thanks to all who offered suggestions.