I have an 8 3/4 "489" case that is missing a cap. Is it acceptable to directlty swap a cap from another 489 case to replace the missing one, or do I have to have it machined to fit like a MW cap? This will be my "street" center. I have a 742 "race" center that will be getting the MW caps.

BTW,
1. How much machining does the typical MW cap need to work?
2. Does anyone have a part # for ARP studs and nuts for stock and /or MW caps?