Spec u header & O2 simulator install question

So I’m in the middle of an engine swap and have some URD spec u headers to throw in, my question is should I put them on the new engine before I lower it back into the truck or wait until the engine is back in and bolted up to the trans and motor mounts?
Just looking for the easiest way

I also have a O2 sim question, in the instructions I got it says “rear O2 simulator” so does that mean the o2 sims that are on the Y - Pipe? I’ve been looking on their website and I don’t see any options for a “front O2 sim” so I’m a little lost as to what I should do. Where should I plug it in at? And will I need to get another dual O2 simulator so all 4 sensors are dealt with?

 

Install them before you swap in the engine. You’ll regret it if you don’t.

 

Sounds like a plan

 

I just did the exact same thing this past weekend, my 05 had head gasket issues so I picked up a '15 engine and swapped it in with the URD headers. If you purchased the headers that don't have provisions for the air injection system you'll need to change out the exhaust head studs as the upper ones in your picture are far too long for the URD headers to bolt up to. I used a set of ARP manifold studs made for the ls series engines.

To answer your original question, definitely bolt the headers up first and then put the engine in the truck. Keep in mind that you're going to have to unmount the drivers side headers and move them a bit to fit the starter back in so don't torque them down until you're done with that.

 

I can take the studs from the old engine right?
Edit just swapped old studs into new engine easy pee-Z

 

I also have a O2 sim question, in the instructions I got it says “rear O2 simulator” so does that mean the o2 sims that are on the Y - Pipe? I’ve been looking on their website and I don’t see any options for a “front O2 sim” so I’m a little lost as to what I should do. Where should I plug it in at? And will I need to get another dual O2 simulator so all 4 sensors are dealt with?

 

Only need the two for the rears. Front sensors are the main air fuel sensors. Rear two are used to check the front cats.

 

Pm incoming for some questions.