All right, I managed to get it pretty much back into shape by using the wooden 'buck' method. I also disassembeld the strainer and straightened its main frame and the mechanism is now 100% operational (the tension rod is still slightly bent right under the head but that's not really noticeable). The central groove is still not perfect round but I guess there's not much more I can do to it. I'm posting just a quick pic I took right after I put it all together to test the sound - and it sounds fantastic to me btw :D Remains only to clean it up and to show it some stick after all those attic years. Thanks again to all for the useful advice!