Your pattern 1856 two band rifle is probably a Birmingham product and the parts WILL NOT interchange with the guns made at enfield or the London Armoury which had interchangeable parts. The pattern 56 band, the lower one, will not interchange with the lower pattern 53 band on the three band rifle. The iron trigger guard has the long lower tang with the rear swivel attached, The brass pattern 53 has the swivel on the front of the guard and is much shorter. I'll bet yours has a lug for a sword bayonet. The lock wont interchange nor will the internals without being fitted.
The only place you will find the lower band is from Lodgewood Mfg and they only have repros that must be fitted but can be done. I searched high and low, even in England for the lower band and ain't none to be had.
You probably won't find the trigger guard except repro that will have to be fitted. S&S firearms is a good bet for both. Look at your rifle, top of stock in front of the butt plate tang and see if their are any markings in the wood like HS an anchor or crown. Look behind the lower guard tang for the same type markings...very important if they are there.
This would be a CS purchased gun, should have the number "25" twice in the proof marks on the side of the breech. That is 25 ga or .577 caliber. If you can post a pic of the proofs, I can tell you if it is a Birmingham product.
If it may be offered to sale, I would be very interested, love to see some pics...Hope this helps..Carl