newbie tube shape cutting question

[owas]

I need to weld up this item,
but i wanted to know how people go about cutting the curves on the box section to fit around the pipe?

i currently only have an angle grinder and a cut off saw.

 

[PhillipM]

Angle grinder + flap wheel.

 

[500e]

http://www.minitruckinweb.com/tech/chassis/0710mt_tool_buyers_guide/photo_15.html
Lots of tools out there

 

[Jim_gsxr1000]

grinder and flap disk is fine if you dont want to fork out for a fishmouthing machine, just make a masking tape template and stick it rount the tube to be cut then just grind inside the lines

 

[stuvy]

if your feeling keen a holesaw on a drill press and some cutting fluid and youl be done in no time

or the easy way is what jim mentioned