RE: Injectors
I ordered a set of used injectors (from vanagonparts.com ), had them rebuilt
and had them put in, zero downtime.  Then had a couple of the injectors I
took out rebuilt for spares.  Did my rig need them at 120,000 miles?  I
don't know, but since the change my '90 is running better than it ever did.
But others things were done at the same time so the improvement may not be
solely due to the injectors.  And one of the rebuilt injectors went bad in
about 150 miles and had to be pulled.  Overall experience very positive but
anecdotal, YMMV.