the Model 19 is a K-Frame therefore perfection, NEVER...EVER pass a K for a J. - Gulliermo
LOL - No argument on there being a difference in shooting a K VS the J frame. As an LEO I have owned, carried and shot both since the 70s. They are performers with a slight edge going to the larger K frame as far as smoothness. The flat spring VS the coil spring definitely has a different feel. And for most, the larger K frame VS the J frame with standard grips fits larger hands better.
However, I have also been partial to the smaller J Frame for back-up and off duty carry. There is a difference, especially if your using an ankle holster. Over that time I used IWB, OWB, shoulder holsters, and ankle holsters... The J frame just works for me. With practice it is an accurate piece that will definitely do what it was designed to do.
I recently picked up a like new, 1977-1978 mfg 3 inch heavy barrel Model 36-1. This little gun is a pure pleasure to shoot. The 3 inch barrel carries as easy as the shorter barreled versions and the extra sight radius picks up easier with my older eyes in play.
As far as the OPs question on his flat latch. Looks like what you have is a functional early Model 36. In its condition - it really doesn't have a lot of high dollar collector value. If it was me, I'd have to bring it back to its former glory and do the full restoration from a reputable smith. David Chicoine has been working on my guns since the early 80s and has even custom built a couple for me
www.oldwestgunsmith.com He is reasonable on cost and is one of the best. In fact, if you have a vintage S&W and call the factory - Dave is who they will refer you to.
As far as cost - you may save a few bucks on the bead blast over the nicer blue. Over the time you will probably own the gun, that cost will be negligible. I'd get what I really wanted and not worry about that.
Guess it comes down to what you want to carry.