The usual way of keeping roller lifters oriented right is with a hinged strap between lifter pairs. A steel (not iron) cam is required. Ken Roddenbush was working up such a rig, but I haven't heard if he ever got it going.

R cams float the valves at around 6000 rpm with the standard springs and 1.51 ratio rockers (which is the design spec -- most Volvo rockers do indeed come in at less than that). With double springs and 1.6 ratio rockers, you'll want stiffer pushrods. You will very likely need to cut down the tops of the valve guides as well.

The reputation Volvo cams have of wiping out lobes is because of excess valve lash and poor adjustment technique.