Those older Cummins 6B engines have a different size injector body than the more modern ones. I believe 1991 (or so) was when they changed.
So yours are probably the 9mm diameter ones (newer are 7 mm).
That means the older ones are rarer. If it were me and I would go rebuild.
However, the reason Cummins changed was to put more material into the head in areas that has thin cross section. Those thin areas had a tendancy to crack.
Not trying to scare you about the cracking as I don't know how common that really is but running cooler might mean you should investigate.
Hopefully Ski will chime in here. If he doesn't you should send him a private message to read this thread.
BTW I had a pickup truck with a 9mm injector engine. I hopped it up and ran it pretty hard and the head was not cracked when I sold it with almost 200K miles.
New Port Richey,Fl