Is there any trouble running the hydraulic roller lifters in a magnum engine to 6500 rpms? Will they work ok or should you be looking at after market lifters?

if the springs match the roller cam should be no problem at higher rpms

magnum stock springs wont cut it

I run my lunati roller with comp 901-16 springs and have been 6200 with no float with stock roller lifters,PR,stamped rocker

cam was nosing over after 5500 but no float at 6200

and they got well over 150,000 miles on them from a jy engine,when I swaped them in in 06

IIRC Jesse Lackman has had them up near 7k without problems. it all depends on valve springs and valvetrain weight (a stock magnum 1.92 dia, 8mm stem is MUCH lighter than an LA 2.02 dia, 3/8 stem valve, stock rockers are much lighter than ductile iron, etc)