Have you watched any straightening vids on YouTube?
I just picked up my 4 alignment pucks today from a machinist.
And using 30mm stainless steel round bar for the alignment bar.
The two center pucks fit perfectly into the carrier, and simply clamp in place with the bearing shells.
Once you slide the bar in, use the diff center as your true straight reference.
The bar on one side was actually touching the inside wall where the bearing seats!
And much the same on the other side....
The outer pucks are only used a center reference.
Once you have straightened the housing, the puck (perfect size match) Should be able to be slide into the bearing location smoothly.
I do not recommend using flame/ oxy.
If you have to, Do not heat the bearing area, or heat only a small area.
This will cause the tube to kick sharply in one spot, thus kicking the true bearing alignment out.
Spread the tension over the length of the bend.
And do not load the cast housing . Chock or load just out side of the housing where tube starts.