You can use 9/16" or 14mm Wrenches.
The Wrench Head thicknesses may need to be thinned. That can be done on a Belt Sander.
Hazet Valve Wrench Head thickness = 0.242, this is thinner but close to 1/4 of an inch.
If you are willing to remove the Fuel Injection Hard Lines/Tubing and know how to bleed the Air out of them after you put them back on you can use regular unbent combination Wrenches if the Head are thin enough.
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