Standard barrel length for early Colts was 7 1/2" - soon followed after the filling of the initial military contracts by 5 1/2" and 4 3/4" for civilian sales.
The best 'serious' Colt references I've found are:
'A Study of the Colt Single Action Revolver' - Graham, Kopec and Moore
'Colt Cavalry and Artillery Revolvers - A Continuing Study' - Kopec and Fenn
'Colt Cavalry, Artillery and Militia Revolvers' (1873-1903) - Cochran
'Colt Peacemaker Encyclopedia' - Cochran
And in answer to your question - yes, there 'are' more - a taking up a couple of feet on my reference shelves worth, but these will really help.
Parson's and Serven's books were written well before the Colt archives were seriously researched, and Wilson copied Sutherland's work - later publishing the same later in time, under his own name - and they're worth reading, but the serious research would be done well after those were published.
A thumbnail:
In 1895, the Government called in the Cavalry model revolver for refurbishment when the 5 1/2" barrel was adopted.
This refurbished weapon was to be the 'standard' - with new grips, new barrels and a full reinspection and refinish.
This means that the bulk of those older 7 1/2" Colts that fought the Indian Wars are most generally found with shorter barrels than they'd originally started out with, and with mixed serial numbers - the only series whose numbers were retained being the rebuilds of 1895-1896.
These shortend revolvers got the collector's nickname 'Artillery Colt' from the fact that a few of the Light Artillery units of the Spanish-American war were so outfitted, but the reality was that the 5 1/2" Colt was the Government standard-issue revolver of the time frame.
Vaya,
Scouts Out!