Campagnolo Strada modifications

For my last frame I had the lips milled off and clearances (between the chainstay and the back of the bolt) were tight, but just about OK. My new frame has no chainstay "dimple" so no clearance. chainline is fine.

How much is safe to mill off the back of the crank, currently I have about 4mm of metal left on the crank.

If it's a steel frame, any frame builder can make that dimple in the RH chain stay in less than 5 min.
Best is to remove BB set before you go and see one.
Really a piece of cake and very safe, especially if the builder has a alignment jig/table/device ...