Wrightknife,
Saw your post on Smith-Wessonforum.com, the reply was correct your D prefix s/n was made 1975-76. More likely 1975, as range thru 75-76 was D750001 - D870000, as you indicated yours was D783xxx.
To see if your gun's wood grips are the originals, remove and look for a pencilled or stamped s/n behind the right grip inside, should match the gun.
The fact it's parkerized surprised me, I thought most Model 10s were blued. (This isn't a problem if original; if refinished to parkerized the collector value would be a little less. Gun will shoot fine.)
Late production Smiths have the newer safety features like hammer block and metallurgy will be stronger, so you can shoot jacketed .38s along with lead. Lead semi wad cutters would probably be more accurate for targets.
You can also get more info on your S&W if you post pictures and note any special markings OTHER than the standard ones like the S/N, "Smith & Wesson", "Made in the USA...", ".38 Smith & Wesson Special CTG"; best bet is post pics to Smith-Wessonforum, those guys are sharp.
Here's my pre WWI M&P, made in 1916:
Regards,
Indy45