I'm near ready to re-install the 2-mono cat, main cat, and rear pipe.

What is the preferred assembly sequence? I noticed the flange holes are two different sizes.
1. Should I connect all 4 pieces on the workbench, then install in the car?
-or-
2. Should I install from front to rear? (Not all the hangers would be attached.)
-or-
3. Should I assemble all 4 pieces on the workbench, but not fully tighten the flange nuts until all the hangers are attached? I can see the case where each of the 4 pieces are rotated slightly in the same direction when the nuts are torqued down while on the workbench, creating a misalignment at the front or rear.

I'm leaning toward #3, but open to any suggestions.

Note: I purchased a new OEM rear pipe about 10 years ago. It was for an 84 Rx7, but for those with a built date starting one month after mine's. Everything aligned with the original pipe except the donut hooks at the front of the pipe. With some careful measurements and templates, and short metal bars and vice clamps, I did match the end hooks of the new to the position of the old.

The picture within the picture is for reference how the hanger on the front of the main cat connects. This was post major engine failure (Fall 2013) and hot oil coated the bottom of the car and melted the rubber hanger. I bought a new hanger for the rebuild.

 

#3.

 

Thanks.
I'm a one-person- in-the-house-garage shop. I did raise the car, but only had 12" clearance to slide the assembly under. Not quite in position yet. but it is coming up. Hopefully tomorrow.

 

Me, too - to this day, I can't get my wife interested in crawling under the greasy car to help me out! Honestly, I do this several times every 2 years to pass emissions testing, so have gotten this down to a science. Once the car is in the air and supported by Jack Stands, I can get the old out and the new in under an hours time. Here are the Pro-Tips; (*assuming you're just installing the stock exhaust with nothing under there...)

1) get some cardboard under the car and a separate piece that you can lay the assembled exhaust system on to slide it under more easily. There are a few protrusions sticking out that can get caught on stuff.
2) install the tailpipe onto the muffler, and the rubber donuts onto the hooks of the front of the tailpipe. With this suspended in place, it gives you a pivot point for getting the rest of it up to the engine flange.
3) from under the car, lift the front of the converter "stack" over the steering rod and forward toward where it will mount to the engine. It'll all be loose at this point, so you should be able to snake it all in there.
4) put the studs on the rear pipe of the catalytic converter "stack" through the two holes in the tailpipe. Spin on your lock washers and nuts, but leave plenty of slack to move things around.
5) at the engine exhaust manifold end, lift the manifold into place and onto the engine studs to mount it with your gasket between. Spin on the 4×14mm lock washers and nuts to hold it in place, but loosely. Now go along the catalytic converters and twist them back and forth to remove any tension - this is the one and only time you'll have to do this.
6) starting at the engine exhaust manifold, tighten the 4×14mm nuts down good and tight, but don't overdo it. Work your way back to each pre-cat and tighten that one down, making sure it's not putting torque on the system. Keep going until you get to the tailpipe connection, and finally, snug those down.
7) double check your work and start it up, listening for exhaust leaks. At the exhaust manifold, any leak here will be LOUD. Further back it might be quieter, but run your hand along each of the connection points and feel for heat. Done.

Good luck, and use quality Jack stands and let someone know that you're under there.

 

Thank you LongDuck for the very detailed procedure. I did not see it until yesterday evening after I finished the install. I like your process better than my headache.
My exhaust manifold has only come out when I rebuilt the engine 10 years ago.
I had the #1 mono, #2 mono, main cat, and long pipe aligned flange to flange, blocks underneath to maintain the positions, and loosely connected with gasket between. Everything was sitting on 3/4" plywood which I slid under on top of two 2x4's. Lifting and blocking the board and then using my small floor jack. Once the #1 mono, and tail end of pipe, where aligned the assembly was loosely secured.
I then put on the doughnuts. I also reinstalled the left front and right rear hangers. At this point the board was no longer supporting anything. Once everything was aligned I started tightening from the front working backwards.
Today I started it up.
Underneath there was hot air coming from the engine compartment which dissipated quickly. (I should have opened the hood to test.) But no lateral air from any of the gaskets. A world of difference. I previously had a leak at the exhaust manifold to #1 mono. Between #1 and #2. And both ends of the pipe.
Again, thank you.

My wife was understanding, but not amussed.
The exhaust now stinks the way it did before I put in the high-flow cat.