Just so's you know - the appelation of 'Open Top' doesn't just apply to those various conversions - the Thuer, Richards, Richards-Mason and the precursor to the Single Action Army - the Model 1871-72 Open Top Revolver made by Colt.
There's also a .22...
The Open Top Pocket Model Revolver was made from 1871 - 1877, with a total production of about 114,200.
They were supplied with two different options for barrel length - 2 3/8" and 2 7/8" and featured varnished Walnut grips.
They're seen with blue or nickel-plated cylinders and barrels - the brass frames often nickel-plated or silver-plated and even left plain.
They were well-built, popular 7-shot .22 rimfire pocket revolvers whose popularity would spark the eventual flood of cheaper revolvers known to collectors as 'Suicide Specials'.
Vaya,
Scouts Out!