Just my 2 cents but break in mileage varies great due to type of rings, clearances, quality of piston, retorque, timing and valve adjustments done, etc etc,, but I am usually a very busy boy the first 500 miles and often up to 750-1000.
I have found numerous retorques required as the gaskets bed in & compress, valve adjustments need frequent checks and adjustments, as well as staying on top of timing and fuel. 10 pages on this thread and not gonna reread the whole thing, but just a WAG here assuming cast iron rings and assume proper cyl finish (Cross hatching) But it aint bedded in until it stops burning oil, thats for sure. So get quick bed in and 100 might be okay, But i have never had that kind of success on anything vintage British. IMHO....
We can bench race this to death, but facts and figures tell the tale. Do a wet & Dry compression test and then a leakdown test. That is the final word. You will have to factor in compression ration a bit, but should be simple enough to tell. I can tell by reading plugs and watching the tail pipe.
