Hello,
Here are some photos of an original 85 F1 tank (on the left) next to an original 86 F1 Montjuich tank (on the right).
They are both aluminium alloy.
The Montjuich tank is attached by two bolts at the front, just like a normal steel F1 tank, whereas the 85 F1 is held down by a single strap. There are many other structural differences between an 85 F1 tank and the Montjuich apparent in the photos and the tanks are not easily interchangeable.
Not readily apparent in the photos is the different shades of red between the two tanks.
Hope the photos clarify some points of issue.
FWIW, the Montjuich tank looks identical in dimension to a Laguna Seca tank(i.e. steel 750 F1 tank) but it is aluminium and the LS tank is steel.
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Ducati F1 Tanks 004.jpg [ 2.19 MiB | Viewed 1636 times ]
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Ducati F1 Tanks 003.jpg [ 1.85 MiB | Viewed 1636 times ]
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Ducati F1 Tanks 001.jpg [ 2.19 MiB | Viewed 1636 times ]