I considered ARP as an option if I could not find appropriate MB ones. The 450 ones were very inexpensive and if they have the proper thread engagement, they should be fine. The necked down portion has a spec for min diameter and it they meet the spec they should be good.

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Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT