Rover 3.5L V8 Standard Engine vs Stage 1 Upgrade

Comparing 2 rebuilt V8 Rover engines. 100% standard vs minor upgrades to give it more performance!
We could put a Holley carb on or a big fancy exhaust manifold to make it a lot faster, however the goal was to keep the car looking externally 100% standard.

These two engines Dyno tested under the exact same conditions, same fuel etc.
What difference can these minor upgrades make?

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Engine 1 for factory restored, standard Rover P6 3500 V8.

Engine 2 for upgraded Rover P6 3.5L V8 which was later upgraded to 4.6L
Upgrades:
- Switched out standard 14v heads for 4.6 10v heads.
- Small bit of port work, smoothing out intake ports where they meet the valve throats and the intake manifold.
- Poppet valves fitted to the carburettor butterflies replaced with flat ones.
- Cam swapped to a Newman Phase 1 Mild Cam.