...I used a 1.25" union fitting with the middle ridge shaved out and a 1.5" schedule 40 piece of pipe on top of that that I had split to fit around the upper tube. Put a piece of wood on top and smacked the seals into place! First one took me all day to get done, second one only about 2 hours.
The union fitting has thicker rounded walls and is less likely to damage the seal as you are pounding it back in.
Other than that, you'll need a set of hex sockets.
And patience. First one took a day (well full evening) because I was taking my time to get it right. The second was cake.