My 1918 block is now cleaned off so I can evaluate it. There is some fairly severe pitting around two of the valve seats, although not into the seats themselves, but it looks like inserts are in the plans now.
Can the other pits be filled in some fashion? My first thought was brazing and then file to match the surface. JB Weld might also be possible but I know that almost all epoxies loose their strength in the presence of higher temperatures.
In reality, the pits not directly near the valves aren't going to hurt anything...just perhaps load up with carbon over time. So, should I leave them alone?
I would not worry about it. I have taken apart engs. that have had bad pitting and bad gouges from broken rings and once from a swallowed valve and ran fine after put together
As long as you have good valve seats and the head gasket will seal, you have no problem.