My friend Larry at CIS Flowtech advised me that the Bosch 0 438 100 111 (Mercedes) aluminum fuel distributor can be swapped for the Porsche 928 cast iron 0 438 100 027 unit. The pressures and fuel flows are the same. Larry states that the aluminum fuel distributors are less sensitive to clogging.
I've had had Larry rebuild both fuel distributors in my 1979 928s. I may look to a Mercedes unit the next time.