I'll do some looking in my books, but I wouldn't trust that site, simply because whoever put it together couldn't even manage to get the pics correct. They have an La-5FN identified as an "Early La-5" and an La-5 identified as a "Late model (see cockpit canopy)"
Anybody that can make that obvious of a mistake must not really know much about their subject matter beyond what they've copied and pasted from other sites....
Dave might not have access to the kind of stuff some of us do, his question is actually highly valid and he tried to research as well - just because its a website doesn't discount it (even wikipedia) however the more research the better (to narrow down you know, what is fact or fiction).
As for what I know, most of my books I converted to PDF to research things on the go (or to read when im away), I have no mention of the word "drop" or "tank" in any of my La books or magazines. Perhaps it was being tested or what not, however I only see small bombs in a few photos, no drop tanks period.