It's hard for me to say if this one is a white whale. Maybe a white whale in training. It appears that one seller on eBay has most of these “White-Back” cards — and once they're gone, good luck finding them. The story behind them is arguably more interesting than the cards themselves. According to the seller, they were not cut from Kraft Mac & Cheese boxes like the common Home Plate Heroes cards. Instead, they were printed separately on white cardstock as sample sets intended for Kraft sales representatives.
One representative reportedly kept roughly a dozen sets when the promotion ended rather than following instructions to throw them away (which the seller purchased in late 1987 or early 1988). Additional examples later surfaced from the estate of a former MLB licensing executive. Between those discoveries and a handful of other known examples, hobby estimates place the surviving population at fewer than twenty copies per player.
Whether the exact number is 20, 200, or somewhere in between, these White-Back samples are dramatically scarcer than the standard issue and represent one of the toughest cards in the entire Kraft Home Plate Heroes set. But, for what it's worth, there is no PSA pop report for any cards in this set, so there's a small possibility I've been had. Maybe I'll try to have mine graded and find out.

Whoa, the Sportflics are amazing! How in the heck did you do that?