This is what I know,
Honda Engines are built with floating cylinder sleaves, there is a space between the cylinder sleeve and the engine block that allows for better cooling and lower operating temperatures. This is called the water jacket. This is not a bad thing, but under heavy boost the cylinder sleeves can shift around within the waterjacket, this is a very bad thing. A block gaurd reinforces the cylinder sleeves to prevent the cylinders from shifting in the water jacket under heavy boost.
The internals of a stock engine are built to run within a certain rpm range. This includes everything from the crank shaft, piston rods and pistons, to the valves and valve springs. The reason that we end up reinforcing the internal components of our engines is because we increase the operating speeds of those components and the pressures that those components are being subjected to. A drivetrain that is built to run at a maxium of 8500 rpms will not last very long if you are reving to 9500+ rpms. Increasing the maximum RPM of your engine is a good way to get more power out of your engine. This is true with both Boosted and NA engines. To do this you need to rebuild your engine with lighter and stronger internal components that will allow your engine to move faster with less stress.
If you are going turbo and going to keep your rev limit the same, and not go with massive amounts of boost then I would say, yes you could get by with just a block gaurd and maybe some stronger piston rods and of course adequate fuel delievey and spark.
IMO if you are going to install a block gaurd in your engine block you might as well rebuild the bottom while you are in there...it will save on labor costs if you decide to do it later.