Found my own answer and submitted it to FAQs for anyone else in the same boat. Here's what I learned in case it's not posted as an FAQ.
PRIVATE ONLINE MATCH WITH FRIENDS - SNOOPY FLYING ACE - XBOX 360 (Information courtesy of Mr. Clark Stacey, President/CEO of Smart Bomb Interactive. Formatted and generalized for FAQ’s by RockyMtnLvr on 3/23/2014)
Presuming that all intended players have the game installed, are XBox Live Gold members, and that you have already added one another as friends via the XBox Live social interface, this is the procedure for starting a private match:
1. Start the game, and from the Main Menu, select "XBox LIVE" using the A button. 2. From the next menu that appears, select "Private Match". (You have now created a private game lobby.) 3. Use the LS (left stick) and A button to select "Game Setup" and choose your parameters. 4. In Game Setup under “Session Type” select either “Open to Friends” to play with anyone on your friends list with the game installed, or “Invite Only” to limit your private match to specific GamerTags on your friends list. 5. To invite specific friends, press RT (right trigger). A menu will appear listing your Xbox Live Friends who have Snoopy Flying Ace installed. Select the GamerTag(s) you wish to invite. 6. When a friend accepts your invite, they will see the same lobby, and you will see each other in the list of Players on the right side of the screen. 7. When everyone is ready, select” Start Game” with LS and press A.
Much thanks to Mr. Stacey and Smart Bomb Interactive!