One of the challenges of comparing 50 year old paint that has seen 10,000 or more heat cycles, exposure to all sorts of chemicals, even cold water splashing in some cars on the surface and who know what.
Comparing to one of the under 100 mile cars with an engine from the same engine plant and year would likely the best you could do, and in person. But that would not be real easy and if you looked at two there would very much be a difference. Let's not even get into all of the blue painted items that were added to the engine after it was painted or installed in the car.
Just have to do your best and get it in the "range" IMHO. We've often described, like in other details that make up our cars, a color or finish that does not catch someones eye as being off or different than the expected. That is what we always shared in judging, owner and restoration seminars and gatherings.