Led lamp and resistor
If you ensure that the supply has no large ripple, or noise, or accidentally gets adjusted up, or starts to drift due to age, bad parts, or temperature then yes. It's not the most secure way.

Any number of things could start to go wrong, but it is in theory and practice okay.

*Right off the bat, your max normal load would be 168 * 3W or 504 Watts, which is 100 Watts more than your supply is rated for...*

And at less than 700mA, the VF will be lower as well. You may see 3V at 600mA, or 2.5V or something. So 12 in series may have a VF of less than 36V...

Proper heat sinking of the leds would be needed to ensure that a high temperature doesn't drop their VF causing thermal runaway.

As to your supply being precisely that voltage, is that true under load and taking into account any ripple?

The preferred way, especially for this high power, would be a constant current supply, not a simple resistor btw.