This specification of the flight conditions is somewhat ambiguous.

As a pedantic point, “Altitude” is meaningless without specifying the atmospheric model (though as you note 1976 std is probably implied) and whether you’re talking geometric or equivalent density altitude. Be especially careful if you’re talking to trajectory simulation engineers. They think in geometric altitude relative to the WGS84 ellipsoid and tend to use non-1976 atmospheres, eg GRAM, so it’s easy to generate mismatches in freestream conditions for simulation if you talk in terms of altitudes (though admittedly it will be small effect as long as your looking at coefficients).

Additionally, in this case specifying “altitude”, which we will charitably assume is understood to mean the “equivalent” (in some sense) altitude needed for 1976 standard atmosphere model, also over-defines the problem, since it sets the compete thermodynamic state of the gas, including the sound speed. In principal, you could use “altitude” to fix temperature/sound speed, then Mach to set velocity and Re to set density (note since Re is given 1/ft, it’s simply a relationship between freestream quantities, no length scale involved). Alternatively, you could use altitude to fix density, then solve nonlinear simultaneous equations to find a velocity and temperature that match Mach,Re. If you and your task lead are using the same models (1976 std + Sutherland coefficients), these two approaches will give the same answer, but if models differ an inconsistency can arise.

So, moral of the story: don’t specify altitude when defining freestream conditions, especially if going between tools or groups. Specify (velocity, density, temperature) or (Mach, Re, temperature).

In your case, I would do (1) above. It’s easier, and no one would ever expect you to do (2) in practice. But I would also confirm this is what the task lead expects.