Hmmmmm,.........
Well I've built a lot of engines over the decades SmBlks, BigBlks, Turbo/ Supercharged, Hemis, mopars, chevys, fords, pontiacs, etc.....I kinda break them in all the same,......Assuming the rebuild is a quality, professional level of assembly,.......your double valve springs, may be of concern if the seat pressure is excessive, because the first item on the "break-in" list is the cam,......I'd contact the cam manufacturer and see what their recommended seat pressure is during "initital" break-in, you may have to run a single spring during break-in and afterwards add the second,.....fustrating yes,.....but not as fustrating as a cam "desintergrating" in your engine turning all your hard work and $$$$ to trash!
Break-in, initial,.....pre-oil prior to running, if your car is not equipped with gauges for oil pressure, water temp, vacumm, etc,....add temporary gauges to monitor engine.....including a timing light
double check ALL fluids,....you'd be surprised what you might forget!
Premium oil and filter,....the Mopar HP filter@ $20 is a real nice filter, IT WORKS,......premium oil like, purple, lucas racing oil, etc
Antifreeze/water mix 50/50
Set engine at 0 degrees TDC or as close as possible, check all linkage, belts, hoses, etc
fill fuel bowls on carb, don't crank engine to prime for fuel! attempt engine start, confirm voltage to ignition,.....if your build is on the "money" and done right,....the engine should start, if not start with the basics, confirm fuel, air, spark, timing, compression,....assuming the engine starts, let idle, confirm oil pressure first, check for leaks, oil, water, fuel, vacumm,....set timing to 5 degrees BTDC, set idle, set fuel/air ratio, check fuel pressure, if you can't perform all these tasks with-in 2-3 minutes shut down engine, .....regroup and prepare again, restart motor, complete the above tasks with-in 2-3 minutes, everything all set, using the idle screw, or what throttle idle adjustment you have quickly bring the engine up to 2000-2200 RPM,....let it run at this rpm for 15-20 minutes, while observing the engines performance on any gauges, displays you have, or have added to moniter the engine,...also observe for leaks, be aware of strange sounds, strange smells are common as paint,and other engine coatings "cook",.....if any gauges, readings are suspect, lower engine speed to idle, shut down, allow to completely cool, during this time, check for your potential problem,rectify if any,restart the above procedure, if no problems,.....let the engine run that 15-20 minutes@ 2000-2200 RPM, lower to idle, shut down, allow to cool,.....next day, drain oil, change filter, oil,......start car, let idle, check all operating perimeters, if OK,.....allow car to come up to temp, do a few (dozen) throttle bursts, slowly,.....nothing more than 3500 RPM......let idle, check running perimeters, shut down, let sit for 5 mins, restart, idle check running perimeters, OK?,,,,a few around the block cruises, observing all vehicle perimeters, I like to stay within a few blocks, who cares if I look like an idiot going around in circles!,....cause if I have to shut it down, I'd rather have to push it a few blocks, rather than call a tow, or drag out a tow vehicle because I'm miles out,.......as the engine/car prove more reliable everyday,.....further cruising, with short occasional "pulls", nothing over 3500 RPM, for the first 250 miles, after that nothing more than 4500RPM till the 500 mile mark, at which, I would change the oil and filter AGAIN!, as well as the antifreeze
after 500 miles, start driving the car as you normally would, i'd keep excessive RPM "runs" to a minimum, until I put about 1500 miles on the motor,....avoid any hot/ overheating conditions esp during the fisrt initial 500 miles
OK,....this is my break-in procedure, some might agree, some won't, ....I've never lost an engine during break-in,......now? during a street race, or on the track?,....thats a different story!
Some people are "turned-off" by the initial 2000 RPM break-in engine speed for 15 or so minutes,....but keep in mind, the cam, is the heart of the engine, and it turns at 1/2 the RPM of the engine, so 2000 RPM at the crank, is only 1000 RPM on the cam,......and most cam manufacturers recommend 1000 RPM "cam" speed, during break-in