Bought truck with exhaust pipe cut off and new muffler in a box, parts in red on image are missing.

1. Was going to order tail pipe that comes after muffler online there's two options 4WD and 2WD i currently have 2WD but want to convert to 4WD later on, i wonder if 4WD tail pipe will fit to my 4WD, i could modify the mount if needed.
Front pipe is same for 4WD?

2. If i buy universal catalytic converter that slides in pipe, can it be installed so far from first oxygen sensor at the end of current pipe?

3. If not then should i:
a. cut the welded pipe and grind the weld to use factory design connection (with gaskets) catalytic converter
b. cut off 90% of the pipe and it then use universal catalytic converter and clamps?

I want to keep the truck for a while, and don't want to weld anything to convert it easily to 4wd when needed.

 

Can someone explain what exactly second O2 sensor that comes after CAT is for, does it adjust lean/rich mixture also?

 

I think the 2nd o2 sensor is for measuring efficiency of the CAT.

My gut says you'll end up moving at least some of your exhaust stuff later when you do your 4wd swap, you'll have extra stuff to deal with like transfer case(s) and crossmember, possibly new rear shock locations, etc. shouldn't be too difficult to deal with.

fully welded exhaust will be better than flanges, so I'd skip that thought. You'll want I keep placement of sensors and cat pretty similar to stock locations for proper function.

 

Run 2wd. 4x4 is flatter since it doesn't need to kick up as far to clear the axle. That means you can run 2wd exhaust on a truck that's been lifted but not vise-versa. You can do a V6 exhaust like I have (I wrote a tech topic on it somewhere around here) but it requires some modification and welding.

Clamps are garbage. Weld or proper flange.

Rear O2 means it was a factory Cali-spec truck. It theoretically tattles on converter efficiency but doesn't really work like most ECM things Toyota did. You need it to avoid an O2 heater SES so just leave it in there.

Keep the cat in the factory location. Too far back and it won't get hot enough to work.

I would suggest buying a factory spec cat ($100) a factory spec muffler tailpipe assembly ($70) a new rear O2 ($40) and a universal sensor plug. Under $250, no welding, just solder four wires and bolt everything up.