The problem that you would encounter in trying to use a 261 piston with a 292 rod is one of wrist pin retention.
The wrist pin in a 261 is retained by the clamp on the small end of the connecting rod. The pin in a 292 is retained in the piston by locking rings. The fact that the 292 rod is not split on the small end is a major reason that it is stronger.
To use the 261 piston with a 292 rod you probably would have to shorten the wrist pin and have the piston grooved for pin retention clips or you would have to use buttons to hold the pin in the proper place.
