Started up my fresh 455 just set distributor at #1 and it fired right off ran breakin time didnt have to adjust timing as was the smoothest start up I ever had out of many. After cool down fired it up and smooth idle so had to be close. Change oil and filter mark balancer to 30 and see how far off it was or was not. Pulled valve covers all pushrods spinning nice for a mild build it sounds pretty good the drive will tell for sure
Having a flat tappet Camed motor fire right off is key / paramount in getting the Cam broken in even if you are only running 90 psi break in springs! Cranking and cranking with only a halfassed firing kick taking place now and then can near guarantee shortened Cam life! Congrats on a new heathy 455!!
As long as it didn't overheat, or make the headers glow, chances are the timing was satisfactory. I'm surprised you didn't at least check the timing while you were running it for the 20 minute break in.
Stayed at 160 degrees headers are still chrome did not blue up at all so since it took off on first crank had to be close oil pressure stayed about 70lbs ran it a bit rich on air fuel only leak was my new B4b had a casting hole by thermostat so had to take off and get welded
Checked timing a minute ago and was only off by 3 degrees during breakin time with no vacume advance kind of like hanging a overhead garage door no tools needed
