Glad to hear that you've got it running properly, that's a good result.
Whenever I have done work on the exhaust I usually remove the luggage tray and prop the rear deck up another way - broom handles seem to work
With the tray out of the way I stand inside the engine bay over the gearbox, you have great access to the pipework/silencer and it's even easier to get to the manifold joint. I start from the back (silencer box) and take the whole lot off, it's easier to re-seal than struggling with sections. If you are retaining the original Cast Iron manifold then I'd consider using a nut-splitter on the joint to the downpipe if that's very rusty, extracting & replacing a stud in that position is going to be a fiddly job.
If you are removing the old Cast Iron manifold & replacing with a 4-2-1 tubular system then I'd get some spare studs on hand. Soak the originals with release fluid overnight but even so there's a chance you'll damage or break a stud if you've got steel nuts rusted in place.
Alongside some spare studs I'd also buy some extended brass manifold nuts because they'll protect the ends of the studs which are otherwise exposed to air & rust. My memory is hazy but I think it was Alex on here who originally posted about these and I think they were for the old BL (60's-70's) Mini engine. I bought a set from Ebay.
Brian