S&W Top Break 38DA trigger guard & rear sear - old vs. new question ?

[old top break]

I noticed on the schematic for these old top break 38's there is listed "trigger guard old style-new style" and "rear sear old style-new style" I know the difference between the 2 style triggers and bolt stops, but can anyone enlighten me to what the difference is with the trigger guards and rear sears ?

I have a 2nd model 38 DA with old style trigger and old style 3piece bolt stop (stop, plunger, spring) - what type of trigger guard and rear sear should that take ? I'm assuming it "may" take an "old style" rear sear and trigger guard as well ?

if so, how do these parts differ from the new style ?

I noticed that that one style trigger has an opening in the back where the sear goes into, and it hollow inside like a cavity or channel- while the other one does not ?

thanks