When I did undo them last time, I did it from under the car, but we have here do it yourself garage where is big lift that lifts car up and I can stand straight under it.
Now I would think that hot/cold treatment would be what helps, ice spray of some sort and run engine so it is hot or heat with some alternative method if putting it back together would be too much of work. Some hammering is good thing to do too, but heat + cold or cold + heat is good. Usually threaded rod like part will undo to and this is not what you want, even in your case it is rather same how they will undo and usually impossible to avoid, lol.
Anyway if putting same parts back it is important that threaded rod like part is in manifold, ok impossible to understand what I mean, I miss now two words from single sentence
Nuts should be copper, at least this is information I got from here so heating will be very effective because steel and copper will expand at different rate and as you get them to hot and cold there will be movement in thread and that will break oxide that is keeping it from not turning, hammering when heated helps in this too, but hammering alone won't do nothing.
I don't know how badly steering parts are on way in RHD model, in LHD model you could take downpipe + exhaust manifold both out from car, just and just, but below car there should be something like 1 meter of space. Then it would be easier to destroy that nut.
