I'm all for modding engines, but I just believe that you go like this (for power):
1. I/H/E
2. Head build (mild) - mildly aggressive cam shafts/gears + tune
3. Head build (aggressive) - more aggressive shafts, supporting valvetrain, head work, TB/IM + tune
4. Block (mild) - larger displacement + tune
5. Block (aggressive) - high comp pistons, lightweight crank maybe, forged internals a good idea + tune

Flywheel upgrade a fun idea. Clutch upgrades as appropriate.

To me personally it just makes more sense to do things this way due to accessibility to head/block for labour, power gains, laws regarding engines swaps (block numbers), being able to put a built head on a bigger block if you need more power later etc.