im running the 4070's on my xr and im happy with them, bit tight fitting in my engine bay but xb onwards would be fine. some clearance issues with the bolts into the heads, nothing a die grinder and carbide burr couldnt fix
pacemakers are better flowing with their pipes and cones

just a basic street motor,351c, flat tops, closed chamber heads, 4v valves, crane hydraulic, elec ign, 780hp holley. made 234rwkw's

hey Ash,

Genie were the go a few years ago, since Pacemaker picked up their tune,flow rates, bends, they are the pick over here in Tas', most our big HP donks have them!
I'd go 2nd hand Pacemaker with new coat of paint if got no rust or damage.

cheers
bruizer