伊507 "Lorelei" Japanese submarine...did it exist? (pix)

A while back there was a topic about Japanese subs, and at that time I had just seen some ads for a new sub movie coming out here in Japan this March (March 5th, actually).
The movie is called Lorelei, the Witch of the Pacific, named after the sub I-507 (the kanji in the topic title is "I," pronounced "ee"), which according to the story was frantically hunting around the waters of Tinian for the ships carrying the atomic bombs bound for Hiroshima and Nagasaki.

Here's a couple of pix of a little Kaiyodo 1/700 model of the I-507 I picked up at a convenience store for about $2.50 USD the other day:




Nicely detailed little model.

According to the info sheet that came with it, this sub was built in France, later modified in Germany, and finally taken over by the Japanese.
It was 110 meters long (about 366 feet), and displaced 4,303 metric tons (4,841 US tons) submerged. In addition to torpedoes, it was also armed with two 203mm cannons in a forward-mounted turret. It was also equipped with a torpedo-armed N-class minisub, stowed aft of the conning tower.

Question: Just how much of this is true? Was it all just created for the film? I'm no sub specialist, but I've never heard of the Lorelei, I-507, or of any giant Japanese subs of French/German origin specifically hunting for atomic bomb transport ships in August of 1945. Nothing in the information that came with the model indicates it is fictional, however.
What do you submarine and Pacific War experts think?

I know, I could do a Google search, but where's the fun in that? I'd rather hear what you guys have to say.

Hope you enjoy the pix, and thanks for any info!

UPDATE: April 2005 I have since seen the film, and it is entirely fictitious. Good movie, too! Check it out if you can.