timing on 67 273?

I would follow iskys specs for break in lash settings. call them and ask.
I would re-check the valves lash settings once the motor hits operating temp.(hot)
Then continue the break in.
I would set the total timing at 32 to 34 for the break in.
I always liked 20 to 25 minutes at 2200 rpms.
Do 10 minutes and then check the rocker arms and 10 to 15 minutes more.
Keep the engine cool....make sure you keep filling the water as it runs and the stat opens up.
Cool motor...........I always wonder if i will build my original 273.