What was this originally and what was done to it by whom, when, where and why?
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Experts?
Easy bit - Alfa.
Edit - 6C 3000 CM, chassis 00125, registered MI 212039. Originally bodied as a coupe by Colli. Factory 1953 Mille Miglia entry and driven by Fangio at Le Mans; crashed, rebodied by Zagato as a coupe and then turned into a spyder. Raced by Scuderia Bonnier, hence the paint:
(http://www.collectorsquest.com/uploads/blog/2012/03/3000CM-1953-00125.jpg)
That's the car, yes, after it was rebuilt (by Zagato I believe) following its accident.
It now has a different nose, which I believe it acquired also around 1956 but no-one really seems to know why; perhaps it had a cooling problem with the original nose.
Original photo: