I've had clearance issues with Crane ductile iron rockers and others over the years. Aluminum rockers are worse because they do tend to have more "meat" to maintain strength with aluminum. It's possible to experiment with smaller diameter springs and retainers, but beehive springs have made that problem easier to overcome these days.

The OEM head design is part of the reason why race heads, particularly W-2's, were modified to work with rocker shaft blocks where the shaft could be relocated. It was to clear larger race valve springs and retainers as well as to get the proper geometry with taller valves.

Watch how you clearance the rockers because they can break! I had some iron Cranes break after clearancing after several years. But I also noticed that I left a "corner" at the top part of the relieved area instead of blending it smooth. That provides a perfect spot for a crack to start.