Welcome to the forum and a big thank you for the fine pics - sure makes things easier.
You have a 2nd Model AUTOMATIC EJECTING 3rd Variation - IDed by the patent date string on the top rib - this variation was apparently only made in 1893. To see the actual serial number, you must remove the cylinder - it will be stamped under the top strap and may include a letter prefix. The letter prefix will establish a year of manufacture if there. (NOTE: H&R used a series of letters on several models just before and right around the turn of the 20th century - not the same as the letter year code used beginning in 1940.) As you surmised - it was made to handle BLACK POWDER cartridges only - .32 S&W and .32 H&R LONG (made obsolete by the introduction of the S&W .32 LONG).
The standard offering for this model is Nickel plated with a 3 1/4" barrel, either 6 x .32cf or 5x.38 cf, molded black hard rubber checkered grip panels with the H&R target logo.
Options are: 2 1/2", 4", 5" or 6" barrels, BLUED finish (scarce) and grip panels of checkered walnut, Mother-of-Pearl or Ivory (I know Ivory was offered as it shows in the catalogues and I also have a set that are numbered to a mid 1890's Auto Ejector.)
You stated that it looks like someone "sanded the frame", needs a trigger return spring and the auto ejector system doesn't work - all of those detract from condition and presently your piece would be considered in the FAIR- to POOR range (60% or less finish remaining and parts broken or defective in some way.) Those factors make your piece worth in the vicinity of $95 to $110. Not much I can do to fluff those values - even with the "blue finish" premium addition. There are "enough" examples of this variation in the market place that better condition pieces can be found by collectors and that keeps the collectibility of your piece fairly low. FIX it up and enjoy it.
The parts you need can be found at the NUMRICH/GPC on-line catalogue. I didn't check, but you should find those parts, as well as a blow up diagram here: