You want a 50 watt vintage plexi head, or even 100, which has more balls. You can pick up a Marshall JMP45 amp for pretty cheap as has been said +1 on that guys. Bear in mind you'll have to have a stack amp on very loud, near full as well to truly replicate the angus tone, it's utterly sickeningly loud, to the point where it burns air.
Another alternative is to buy a second hand Cornford 50 watter head and cab, it might be outside £600 but it'd be the bollocks! as they are hand made like the first original marshall heads back in the day.
later,
Ben.