318 LA rebuild after losing a valve seat

No... It is nowhere near 100 grams change! That book is wrong. Geezzz... Now if you weighed the parts and do the bobweight computation wrong AND had worst case variations you still could not get to 100 grams off.....
I have weighed both sets of rods. There is 32 grams difference on average (726 vs 758 grams per rod), which numbers have confirmed by others, and most of it is in the rod beams. If you weigh big and small end weights ( which I have done), most of the beam weight goes into the small end weight. When you compute the bobweight, the small end rod weight is cut in half, as it is part of the reciprocating weight.
So trust me on this one... The bobweight change is in the 30 gram range. I have all the numbers to show it. For a mild street car, it will run OK.
Now if you want hotrod quality, then it ought to be balanced regardless.