Not sure if you really could tell if noise is coming from bottom end or not but being the engine used to have boost and the amount of miles on it I would first suspect the valvetrain including weak springs

You could still use the water/methanol even with engine NA, I have on my vette for years now.
At least it would clean and then keep cylinder/valves clean as carbon buildup will induce more noise along with knock as carbon gets thicker.

At least pull the valve covers would allow you to check at least for maybe weak or broken springs, esp if there are dual springs as the thin inner ones tend to break.

I would think the compression and leakdown tests would give you a good idea are parts you cannot see how well or poor the internals are.

Too bad it is tough getting parts in your country as a LS2 or even LS3 would work and even stock they put out more HP/Tq then your LS1.