Hi Leigh,
the Yorkshire Hussars originally wore the Light Dragoon helmet i.e. the Tarleton, but changed to a shako in 1817. According to Carman the Busby was adopted in 1856 and was worn from then on.
The Yorkshire Dragoons adopted a white metal helmet, of the 1871 pattern, in 1876 and it is interesting that it had the acanthus leaf plume holder, associated with the 1847 pattern helmet. The fluted plume holder came later.
The 2nd West Yorkshire Yeomanry adopted the 1847 pattern helmet just before the Crimean War - I don't have a specific date.
Carman's book on Yeomanry headdress has a photo of an East Riding tschapska that has a quite different plate to mine but then describes the lance plate that mine has.
There is a lovely illustration of an officer of the East Riding Yeomanry in a book by R.G. Harris 50 Years of Yeomanry Uniforms.
It also appears that the lance cap was worn only by officers and only from 1906-
I have had a couple of big wins on eBay but also a couple of duds - one so bad that I sent it back. These days I have dealers (whom I trust) offer me stuff which often comes from their private collections. Never cheap but always of good quality.
I know that you, and Graham, are keen on the Northumberland Fusiliers. If I see anything will let you know.
Stuart