In drafting an indictment for manslaughter, is it sufficient to allege the defendant recklessly caused the death of the victim "by operating a vehicle/heavy machinery with illegal drugs in his system", or must it also allege the actual act that that resulted in the death (e.g. "failure to brake", "failure to keep lookout")?

This is a RR case so Intox Mansl is not an option.

While the labs will show illegal drugs in his system, they may not be sufficient to prove intoxication BRD.

So, is the contention that he was reckless merely by operating the vehicle/heavy machinery with illegal drugs in his system sufficient without attaching it to some other specific act such as failing to brake?

How about "operating a vehicle with illegal drugs in his sytem and colliding into another vehicle"? Must we have another means such as failure to brake or failure to maintain safe distance, etc?

I think you need to allege the conduct that caused the death: failure to keep a proper lookout, failure to maintain a safe distance..., speeding, failure to brake, etc. Simply operating a vehicle with an uncertain amount of an illegal drug in his system would not necessarily be reckless under the legal definition.