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An alloy/carbon fork is probably between 600-800g
The 4ZA Ellyps/Alpina thing which everybody has on their PreCursa among other things is about 550g with a modest steerer length. This cheap all carbon Focus fork is sub-400 uncut, so the opportunity to lose weight is probably more like 150g for cheap or 250g if he gets a high-end sub-300g fork.
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They claim the MASH fork is about 620g.
Cinelli claim between 500-550g which is about your reckon.
An alloy/carbon fork is probably between 600-800g, full carbon with a small headtube should get the fork weight down as much as 330-340g.