Congrats on your new K serial Model 17-4 !

in 1977 the dash 4 variation saw the the gas ring move from the yoke to the cylinder ,
1982 S&W stopped the practice of pinning the barrel to the frame and recessing cylinders on magnum handguns ,
Apparently it did not warrant a dash number change as dash 4's are found both pinned and unpinned.

Sometime before the dash 5 revision in 1988 they also changed to a 3 letter serial prefix and moved the S&W trademark from the right sideplate to the left.

Wood Magna stocks also got noticebly large and blocky at their base in this era as well.