Wilf,
My guy said a similar thing. Run it at around 2,000 rpm for 20-30 min (cam break in) and then start pulling. I have a friend that had a 351 stroked to 427 a few years back and that is how they did his. He now has about 10,000 miles on the car and most of them are racing miles. still doesn't use any
oil and compression and
oil pressure just like the day it was built.
When I lived in the UK, I had Real Steel dyno my SBC and they more or less did the same. I wasn't there when they did it, but that's the way they described it.
Love your Crendon. I had a RAM from Adrian Cocking when I lived there. The Crendon is a cut above the rest.
Mark