<<Disclaimer: Verify this information before applying it to your situation.>>

Thank you to everyone for responding.  It helped to clarify some of the
recipes I have found.  Sorry I have taken so long to summarize.  Things have
been busy around here.

Noninstant dry milk is a fine powdered dried milk, not the instant kind.  It
is usually used for baking.

People seemed to have found this in different places such as the health food
store, food co-op, through some of the gf companies, and the grocery
store (in the baking section or it can be found in the infant formula
section).

One person said that it is without a non-caking agent which prevents the
milk from clumping.  The agent may or may not be gf.  If you have a gf dry
milk, you can use that.

One person said that a gf powdered baby formula may be substituted, but it
may have different results.

Two people said that they have substituted instant dry milk and their baked
goods turned out fine.  However, one person did mention that the instant
does not always give as smooth of a baking product.  Another person said
they did not like the noninstant, because it clumped so much.  She uses
instant dry milk instead.  She said that 1/3 c instant is equivalent to 1/4
c noninstant.

One person said instant could not be substituted for noninstant milk.

A few people also said that noninstant is supposed to be more nutritious.