Well, I can help you find info on that line of vintage Orients, but I probably can't point you to the exact case style
First, I'll give you a link to a database I constructed several years ago, that has a vintage Orient section:http://seikoholics.yuku.com/forums/69/Japanese-Watch-Info-Database/Japanese-Watch-Info-Database#.VC9JZ1fhjNE
Just scan down until you find the Orient section of the database & you'll see within it, 2 separate sections for "Grand Prix" ... one was a hand-wind "line" and the other was automatic. The automatics are based on the hand-wind movement.
Now, just by way of introduction, "Grand Prix" was Orients best quality line in the early -> mid 1960s. It replaced the Royal as the "top of the line" movement in the early '60s.
The "Swimmer" designation indicated a more water-proof case than the "regular" (dress watch style) Grand Prix.
The hand-wind Grand Prix came in several jewel count variants and also there were non-calendar and Date variants. I have a hand-wind 25j Grand Prix Calendar (has Date display) in my collection & it appears to be a quite high-quality piece for it's day... though not as high as the top-of-the-line Seiko model of it's day (Grand Seiko with either calibre 3180 or 430 hand-wind movements) ... probably more like a Seiko Cronos Special or Crown Special & maybe just slightly below a King Seiko (1st Generation hand-wind or calibre 44A) of the same period. Again, for details of those, look through my database.
That database is a companion to a Japanese watch discussion forum. It would pay to look through articles/posts in that forum as well (various sections) as I'm sure I (and others) wrote about the various vintage Orients there.
Now, I also have a Grand Prix automatic ... probably Orient's best quality automatic ever (? well, at least thru '60s & '70s) though a couple other vintage models come close or match it as well. Mine is a 100 jewel "Grand Prix 100 Triostat" introduced in 1964 supposedly as a Tokyo Olympics model. What makes it high quality is not the 100 jewels, but the Triostat fine-adjuster for the balance and the auto-wind system which is an IWC Pellaton design! You can find that watch on the database/discussion-forum I've pointed you to. That will help you understand more about the Grand Prix and other related models to yours.
I should point out that the Grand Prix (hand-wind) line used 2 different movement designs over it's life-time. I wrote this up at the site I pointed you to:http://seikoholics.yuku.com/topic/962/ORIENT-Grand-Prix-Handwind-2-types
Also check out some of the other articles I pointed to in the Orient section of the "Auxilliary Database" thread I constructed:http://seikoholics.yuku.com/sreply/5398/ORIENT-Brand#.WCO4APQuM0k