JANELLE:
Good morning. If your cake recipe in your old baking books say to use a 8 or 9 inch by 2 inch deep cake pan then you can use your 6 cup bundt pan.
Because in a regular cake pan it will take 2 3/4 to 3 1/2
cups of batter allowing for the rise due to the chemical leaveners. A 6 cup bundt pan will hold 4 3/4 to 5 cups of batter allowing for the rise. Remember to grease the bundt pan well & do not remove the cake for about 45 minutes after it is removed from the oven.
Enjoy the rest of the day young lady.

~CHEF DUNASK.