318 LA rebuild after losing a valve seat

You put the dots at 6 and 12 and just put the distributor in to fire #6. No need to do anything else, unless you want to waste time.
I don't fully agree on the need to change valve springs for break-in. It depends on the cam and the actual springs. If the open valve pressures are under 300 lbs, I don't bother. Having the proper level of ZDDP in the oil is far more important if your springs are not too stiff. What springs and cam is this? Or is that info back on the thread?
RRR is right on the likelihood of piston to valve contact. But always check. You can buy some light hardware store springs for that task.