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?

The cap is not a direct swap so it would need to be machined BUT the cap heights are not uniform so it would be hit or miss for you to find one that was bigger than you need to machine down . I used an MW cap once , had to take about .120 off it before doing the final machining. Steve if you were closer I have a bunch of empty cases and I let you have one cheap ...

Where are ya ?

still freezing my butt off in new england

I don't think there is a stud set to suit the 8-3/4", I used a stud kit for a 9" the stud itself is a little short but still a lot longer than the original bolts.