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Yes they can be prone to breakage when used with roller cams. Typically when one goes there tend to be more afterwards. Yes they were made by Dove but they went our of business or were bought out. Those are a 1.6 ratio if they are blue and 1.5 if they are black. They are the same as the big block rockers so you need to know if you need a left offset or a right offset. (which side is the adjuster on). I should have some spares if you want just one. IF you are running a roller I would invest in some better rockers, Harlands or T/d would be your best bet.
They were made from an extruded aluminum and for sure have a cycle life like most aluminum parts.

Todd