Help with the derusting cure

A beautiful good evening together, on my beloved elk there has been an unsightly spot on the underfloor since I took over it: the area around the end pot. The rear bumper holders can almost be removed with the toothbrush and the exhaust suspension is kept together only by the rust – so far no problem, the places are probably the classic par excellence, as regards rust in the 850s. The bumper holders are easy to recreate for small money. The more serious problem, however, is the following: even the rear longitudinal beam above the exhaust has not been spared from the rust! It is stable, you can hardly scratch something and you can not push it twice, but nevertheless, more or less superficially there is a good trace of rust on it. I would very much like to deal with the whole thing in a timely manner and the rust spots sometimes on front man b But now I would need your help in two places, for that I would be very grateful: 1) Does anyone happen to know if there is still to buy the guttered exhaust holder? Volvo number is 3547625, unfortunately there is nowhere – the only thing to find are repair kits for the silencer side, but the underfloor suspension probably falls off at some point… 2) What is really important: what do I do with my longitudinal support? In any case, the option is not available: leave it as it is or still drive down and is good. Would the car like to keep for a long time, and as far as I can see, this is the only place that could become critical for a short or long time. Could one do such things like dry ice, glass, sandblasting? Or rust transducers? Or mikesanders’n? And above all, to which place could one turn with it? Body construction? I thank you very much in advance for any Help me, I would find it just too bad if the Volvo would go into the krätsch in the long term because of such an annoying problem and unfortunately I am only little familiar with the subject of bodywork so far. In the appendix still two pictures from below. Many greetings, Nikolai