Not that complicated actually- as for hussars, they originally started out with a "mirliton"- a sort of conical fabric cap. This evolved into the shako for most, but in emulation of infantry elite units some went for the busby, which is basically a cavalry variant of the bearskin.
The French had them for the elite companies in each regiment (also in the Chasseurs a Cheval) and for their Guard chasseurs, the British just handed them out to whole regiments at the end.
As for Grenadiers, originally the elite companies of regular line regiments were grenadiers, for which the fashion became bearskin caps.
Guard units were often called grenadiers (all elites, after all) and so wore bearskins too. Due to economic concerns, the French at least stopped issuing bearskins to line grenadiers, though many regiments managed through informal means to keep them for their grenadier companies.
In practice, this means that there is no significant difference between a line grenadier and a guard grenadier in their uniform, and certainly not at 1/72 scale. The figures are interchangeable.
Hope that helps!

so a set by zvezda named imperial guard can be just grenadiers,because thats what i was leaning to.

busbee is correct term for headgear and at some point french hussars wore them.

thanks for reply

tom

Until about 1809 Guard and Line Grenadiers wore the same Bearskin cap. Thereafter, only the Guard wore bearskins. To complicate matters, bearskins were only worn by the Old Guard Grenadiers (with front plate and red back patch) and Chasseurs (no plate or patch) The Middle and Young Guard wore shakos.

Other distinctions were that the Guard had blue collars, red turnbacks and red cuffs with no piping and a white button background. Line Grenadiers had red collars with white piping, white turnbacks, red cuffs with white piping, blue button background with red piping.

oh this helps a good deal and thank you.before 1809 from a plastic soldier point of view poses with bearskins could be both line and guarg.after bearskins only for guard.
thank you
tom