A few things to consider:
There is no obligation to participate...if you don't, you won't be able to win a dang thing though.
The cards pictured are not the only ones that are available to utilize your credit towards. Here are links to the 11 listings on the BST that picture all that is available (of course cards that indicate SOLD or PENDING are not available).
http://www.net54baseball.com/showthread.php?t=274062
http://www.net54baseball.com/showthread.php?t=274064
http://www.net54baseball.com/showthread.php?t=274066
http://www.net54baseball.com/showthread.php?t=274065
http://www.net54baseball.com/showthread.php?t=274060
http://www.net54baseball.com/showthread.php?t=274063
http://www.net54baseball.com/showthread.php?t=274061
http://www.net54baseball.com/showthread.php?t=274250
http://www.net54baseball.com/showthread.php?t=274067
http://www.net54baseball.com/showthread.php?t=274070
http://www.net54baseball.com/showthread.php?t=274069
Below is an example of what a guess would look like. None of the below issues are part of the current Brockelman Auction NOR on the list I provided, but if they were, and I didn't consign any cards from these issues to the auction, you would have all 10 correct and vintage cards of your choice would rain upon your head like a flightless pigeon.
Your Guess will look like this:
1936 Goudey
Uncle Jacks
T202
W560
D310 Pacific Coast Biscuits
National Game Card
C46
T215 Pirates
E105 Mello Mint
E126 American Caramel