I don't personally think you need 1000 miles these days to run a modern engine in. Bearing tollerances for con rods and cams a pretty spot on and the materials longer lasting.
Your mechanic is correct about the boost level. you don't want to run it on high boost (if any) during that first period.
What ever you do, do not just cruise around a motorway. Running in the engine is mostly about bedding in the piston rings so that they fit the tiny inperfections in roundness of the bores. For this you need pressure acting under the rings to force them onto the bore walls. The crosshatch pattern of the bores when new do the microscopic cutting, so to speak.
I recommend taking the car to a clear road literally only a few miles from starting first time. Drive to about the 4000prm limit on about 3 quarters throttle and then back off. You want to carefully force some pressure into the cylinders and then have it coast down so there is a fair bit of engine braking. Most of the running in period is done in the first few miles for the piston rings. I'd then change the oil after that first period and run around varying the engine speeds and building up the revs after that. A motorway will just be a constant light pressure in the cylinder. Country roads with gear changes are the best.
hey htc hows it goin.
i know your the guy to ask. ive nearly completed my engine rebuild bt project. ive heard so many tales i wana ask you how do i run in my engine. my engine builder has said he will give me the car running very low boost ( if any lol ) with the running in oil and i must drive within 4000 rpm 4 500miles change oil then afurther 500miles, then map.
i dont know whether i should do this day to day or just sit on the motorway as this quicker
thanks for reading hope i haven't missed any thing just message me