470 runs out of steam at 5100 rpm

Well the cam seems a little small to me but I ran a 241/247 hyd flat tappet in my 470 a few years back and it would pull hard to 7000 rpm so the cam is probably close enough to work. I would wager that it is valve train instability but it might be ignition related. I've seen the chrome box just give up at 5000+ rpm before. I've also seen guys who use those ignitions and make power but I've never had a lot of luck with the old Mopar Performance boxes. Maybe borrow a MSD billet distributor and 6 box from someone and see how it works. If that doesn't make any difference then it is probably the valve springs. When you use a hyd lifter in a performance application you have to get everything just right or else the lifter collapses under load and the lift goes away. You need plenty of oil pressure and the correct oil to keep the hyd lifters happy at 6000+ rpm with stiff valve springs.