Hey Wilf!
I do not have first hand experience on this howevery I will recount the information given to me by the previous owner of my ERA. The engine was broken in and tested on a fluid dyno (flywheel connect not wheels) at the engine builder (Danbury Competition Engines) back in 1992. The engine was run for about 4 hours with one
oil change at one hour and another at the end of the process. The engine was cycled thru various RPM ranges and not tested for max HP during the procedure. The carb was tuned at the end of the process while on the dyno.
I do have photos of the process (not digital) which show the ERA headers as being what appears to be red or yellow hot, but not being there in person, it could be just a photo feature.