Anyone know the diameter of 4.0L exhaust manifold?

Anyone know the diameter of 4.0L exhaust manifold tubing?

My truck is throwing the code for inefficient catalytic converter (P4020). I tried the acid bath wash on the cats and sensors, but the engine light came back on.

I don't really want to cough up the $1200 (Canadian) for new cat/manifold and can buy an aftermarket OBD II one for $50. I'm going to try cutting the old one out and welding a new one in. I just need to know the diameter of the tubing before and after.

Not sure why Toyota decided to put the cat right into the manifold on this truck, makes for a very costly repair, or maybe that was there plan.....It's the only one out there like this (not the 4banger or the Tundra).

 

I'm not math guy but I think you can take a tape measure, get the circumference and divide by 3.14 and it gives the diameter.