Don,

Two tips that meant the most to me during this phase in body work.

1)  After priming waft a little black (or contrasting color) lacquer
onto the surface from 2-3 feet.  This will give you a guide coat.  As
you block sand all the lacquer should disappear.  That which remains is
a low spot and can be scuffed then either reprimed or filled.

2)  I used Spot Lite from my local PPG store to fill the larger
imperfections.  It is micro based, fast hardening, a different color
(also helping imperfection discernment), and light to sand.

Finally, I would go over the final body work with a perfect coat of
primer to minimize any variation of your color coat.  This single color
primer is key when painting especially with the lighter colors.  I used
red top coat also. One alternative is that your paint shop could
recommend a compatible sealer to do the same.  I am told that it can be
sprayed immediately before color without sanding.  Haven't done it
however.  I spent about 5 coats of primer in this process.  I believe I could do
it in 3 now that I'm familiar with how much primer can be applied in any
coat.  Also, every inch of primer needs sanding before the next coat.

As far as compatibility goes, talk to your painter but I'm gonna go out
on a limb here and say that most primers are compatible with fillers.
Exception to this is the thin putty that comes in a tube.  They will
occasionally shrink when painted over.

Larry Henney
N360LH

PS:  There's no such thing as the final stages of body work.  It is
merely the point of exhaustion just prior to spraying color.