Everyone's tips are spot on - I'll add two more. First, when it comes to exhaust system work, if there's any way you can bribe someone to let you use their lift - that's a huge help. Being able to stand underneath gives you all kinds of leverage that just isn't available laying underneath one. Second, if you've got access to a cutting torch - it makes disassembly SO much easier.
I had to break the flanges on my '85 to get the H off the headers. Be extra careful when you're taking everything apart so you dont break anything, or else if this is your daily driver, you might be walking. Get a torch and heat things up.
it will fit with some persuasion from a hammer. suggest you liberally spray down the header flange bolts, O2 sensors, and pipe connector bolts with a good penetrating oil first and let it soak in for 30 minutes or so. also be careful with the O2 sensors, they need to be removed first before you get the pipe loose, undo the wire connectors and tuck the wires up out of the way-don't get anything on the ends of the sensors once you get them out as this will ruin them. hardest part I ran into was getting the crossover pipes to connect some and then getting the flanges connected to the header flanges. its best to barely get the threads started on the upper flanges and then try to connect the crossover pipes. don't clamp down on the crossover pipe until you have tightened up the header flanges on both sides as you need to wiggle the whole assembly some in order to get things to line up correctly and hit the holes in the hanger brackets. some grease or liquid soap on the rubber hangers will ease insertion and also use never-seize on all the bolt threads for ease of disassembly later. I did mine on the ground and it was a real pain, but it can be done this way. an extra pair of hands also helps in this juggling act. if you can get access to a lift, definitely go for it. also don't forget to reinstall the O2 sensors when you think you are finished. have fun and be prepared to bust a knuckle or two, but it is worth it in terms of performance and sound. good luck!