Hello Keith,
Its been a long time since we last talked by E-mail. Thanks for this interesting post.
Checked with the Registry of Surviving Civil war cannon and the paper list I purchased from Wayne Stark and I can offer some information. All four of these cannon are listed in the paper list as being in Midlothian Va. privately owned.
The information you mention for the first gun appears to be correct with the paper list and the book, "The Big Guns" which contains a updated list of cannon locations different from the first edition of the book "Field Artillery Weapons of the Civil War".

The second gun appears in the paper list and and "The Big Guns" as Registry #414 with the oher information you provide agreeing with the list and the book.
This gun also is from Midlothian Va.

The third and fourth guns are actually M1861 3" Ordnance rifles made in 1865. The registry # 855 agrees with the sources but the gun you mention as registry #846 is actually registry #843 which agrees with the sources. Gun number 846 is listed as being in Chicago Ill. The Ordnance Department ordered a batch of 28 of these 3" Ordnance rifles on Feb 1, 1865. This batch contained both of these guns as the batch registry numbers ran from 842 to 869.

I hopes helps you in identifing these guns. Still don't know why this excellent message board went silient. Hope it goes live again.
Ron