If you recently purchased a used copy it should be inspected. If it was released on 4 x 400 - you'll find the original splices.
Here's what happens in theory
The print goes out brand new from the lab on 4 x 4.
At some point the leads are cut and big reels are used.
During the big reel assembly, care is not taken to mark the joins for later break down back to original reels.
When the film is broken down a few years later, reels are wound until they are full, and a new cut is made.
Somewhere within those new cuts are the original big reel joins.
If you can locate those joins, it is possible to reassemble the print to the original 4 x 4 release.
When you find a splice you should be within 400 feet on a per reel basis although that is not always the case. When this happens one thing to look for is between both sides of the splice there is almost always a scene change or jump cut.
It is extremely rare although possible for a reel change to occur with no change of camera angle.
If you are reformatting an optical film you can check the optical track at the splice. A few inches before the splice the track will be silent and show NO signs of movement. As the splice passes then the movement begins of active sound.
Consider this information if you are looking to restore the print to the original 4 x 400 release. And then you will have the reels you are looking for.
If all of that sounds confusing it isn't. Just make sure you have a pair of hand crank rewinds to use for this job.