Inyati13 - All Cats have a factory specified arrangement for roller placement. Most Cats have a mixture of double flange and single flange track rollers.
The double flange rollers improve track chain alignment and location - but they're more expensive, so usually a mixed selection of double and single flange rollers is used.
Some Cat excavators use all single flange track rollers only. All Cat crawler tractors use a mixture of double and single flange.
Some tractor owners will place single flange rollers where a double flange is specified, or vice versa. This is usually carried out as a "stop-gap", "will-fit", or "nothing-else-available", move.
The Cat single and double flange roller specified arrangement is best followed, because Cat have done their research on the best placement of rollers.
It's rare to have a rear double flange roller in front of the sprocket, as the inner flange can come into contact with the sprocket teeth, and cause damage to both. The D3 has to have a single flange roller at the rear.
Here is the scan from the Custom Track Service handbook that shows the correct positioning for rollers, for a wide range of Cat models, up to about 1980.
http://i48.tinypic.com/2vru1a8.jpg