Aluminum roll cage?

[verde2002]

https://losangeles.craigslist.org/lgb/cto/d/1980-bmw-etcc-grrace-car/6734633187.html

This ad claims this former ETCC BMW has an aluminum roll cage. Never heard of that, did they really make roll cages from aluminum at some point?

 

[Markos]

https://losangeles.craigslist.org/lgb/cto/d/1980-bmw-etcc-grrace-car/6734633187.html

This ad claims this former ETCC BMW has an aluminum roll cage. Never heard of that, did they really make roll cages from aluminum at some point?

Material properties aside, does the ETCC allow bolt in roll cages?