I just read Wiley Sword's Henry Rifle Book from cover to cover for the first time on my flight from back East. I have read excerpts, but never the whole thing.
Random observations:
Between 200 and 300 iron frame Henry rifles were manufactured, frames and buttplates contracted from Colt (propbably). It is assumed that these were among the first to see action in the Civil war. Henries (iron andbrass) were appearing starting mid-1862.
Though less in numbers than the Spencer, the Henry was spread much wider throughout the Army than the Spencer as 90% of the Henries were private purchase arms. Virtually all Spencers were issue arms, so you had to be in a unit that was issued them to have one. Henries, on the other hand, were spread throughout the entire army, especially the Army of ythe West. Too many units to count had at least few Henry rifles. Some infantry units had their Henry armed men mounted to use as scouts.
For the most part, Henries began gaining a reputation in mid 1862, at least a year or more before the Spencer was widely known.
Winchester enhanced the popularity of the Henry by using the press (newspapers), causing private sales to exceed his production capacity. Spencer never did go after private sales but did land lucrative government contracts that eluded Winchester. The government contracts allowed Spencer to expand to increase productivity. Lack of these contracts denied Winchester the capital necessaryto expand his facilities. Winchester was stuck at about 200 (give or take) Henries a month most of the time.
The Sword book paints a little better picture of the widespread use of Henries than the Bilby book does, at least in the sense of identifying lesser units partially armed with Henries.
The shear number of Spencers in service at the end of the War (at least ten times as many as Henries) caused many Spencers to be surplused out to the civilians cheap. Henries, on the other hand, had been private purchases, and were never surplused out, but went home with their original owners.