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

Sorry for the delay in summarizing (been under the weather and returned
to work after 9 months sick leave). These are the replies I received:
----http://www.thevision.net/maxwell/html/celiac.html Yummy Yellow cake
recipe I use is on this page.

----Gluten-Free Yellow Cake
Ingredients:
1 1/2 cups white rice flour
3/4 cup tapioca flour
1 teaspoon salt
1 teaspoon baking soda
3 teaspoons baking powder
1 teaspoon xanthan gum
4 eggs
1 1/4 cups white sugar
2/3 cup mayonnaise
1 cup milk
2 teaspoons gluten-free vanilla extract

Directions:

1) Preheat oven to 350 degrees F (175 degrees C). Grease and rice flour
two 8 or 9 inch round cake pans.

2) Mix the white rice flour, tapioca flour, salt, baking soda, baking
powder and xanthan gum together and set aside.

3) Mix the eggs, sugar, and mayonnaise until fluffy. Add the flour
mixture, milk and vanilla and mix well. Spread batter into the prepared
pans.

4) Bake at 350 degrees F (175 degrees C) for 25 minutes. Cakes are done
when they spring back when lightly touched or when a toothpick inserted
near the center comes out clean. Let cool completely then frost, if
desired.

Makes 2 -8 or 9 inch layers

I would convert it into a cake mix this way:

Replace the fresh eggs by egg replacers, following the instructions to
replace 4 eggs.

Replace the milk by the amount of dry milk it takes to replace 1 cup of
fresh milk.

The most complicated replacement is mayonnaise.  You replace it by
butter flavor shortening, but I would check other similar size cake
recipes w/shortening in it and use the same amount

----You can use ANY reg yellow cake recipe that is not gf and works
well, by sub. cornstarch for the flour.

Many thanks to Ann, Jeanine, and Janet for replying. Susan