I started these in the 1970s with one of the light infantry just to see how it would go. The conversion was mainly just some carving and them painting. The plume was a pin thickened up with some nail polish hardener.
I liked the result so much that I ended up completing the whole unit, the grenadiers coming from the AWI British Grenadiers set.
A recent post in the Napoleon’s Battles Yahoo Group touched on these types of conversions. I have a few more I should get out and photograph for posterity.