As
@Ross stated, there are some mechanical parts that cause certain physical limits to max RPM.
All LSJs and LNFs have forged crankshaft and rods (note: Crate LNFs are typically European LHUs with non-forged rods). LSJs have forged pistons. Getting all forged rotating parts into your engine is the first part of the equation.
Getting unnecessary rotating weight out of drivetrain is important, so losing the balance shafts will help. But also losing weight in other places, like the flywheel/clutch are also as important.
Next is fueling. LSJs are easier that the fuel injectors can be sized to match fuel type (if using something other than dinosaur squeezings). The LNF option is Opel fuel injectors to increase flow by 20% and/or increasing the output of the high pressure pump - ZZP has that covered with a replacement intake cam.
Then the valve train. The valves are all capable, but the valve springs are not. These need to bumped to a higher seat pressure spring that can control the valves to keep them from floating at high RPMs. The ZZP valves are reported good for more than 7500 RPMs. Having more aggressive camshafts to enable more breathing capability above 6500-7000 RPM is also a must.
Having a shorter intake pipe before the turbo/supercharger and a better exhaust manifold and tailpipe make for less restriction on both ends of the suck-squeeze-bang-blow cycle also helps.
Keep in mind the RPM capabilities of the clutch (is it rated for 8000RPMs) and the ability of the transmission to shift at that RPM may also be limiting factors.
Having all of these go-fast parts in the engine can get it to spin up higher and produce more HP, but it also will shift the torque higher into the RPM band too - a little less fun on the street and typically a little slower for autox. But this combination would be ideal on a road course where the higher RPM capabilities would be most used.
