Back in the late 1960's the Vietnam war was on and it was almost impossible to get new Pythons.
However, new in the box Troopers and new Python barrels were still available so custom gunsmiths were making up Troopers fitted with Python barrels.
These were known as Troop-on's or Poopers.
The gunsmiths were heli-arc welding up the front of the frame to match the Python barrel, tuning the action, and giving them a highly polished Python level blue job.
After an article appeared in a gun magazine about these modified guns, orders with custom gunsmiths greatly increased.
Today, people think they have an early Python only to find they actually have one of these modified Troopers.
Other than a serial number check, the only indication of an altered Trooper is a slight blush in the blue job where the front of the frame was welded.
Today, due to the cost and difficulty in finding a usable Python barrel, I suspect the cost would be very high. Probably not as high as a Python, but close.
The standard Trooper or the higher quality 357 Model is great as-is, if you can live without the Python barrel contour.
The Trooper Mark III, Mark V, and King Cobra are high quality guns but they aren't a Python. Nothing was.