proper engine break in is one of those never-answerable questions... everyone has different opinions and different experiences.
"use conventional oil, run it hard"
"use synthetic blend, run is soft"
"use synthetic, run it hard"
i suggest changing the oil often... ever 150 miles or so for the first 600 miles.
i suggest conventional oil for two reasons: sythetic oil will by-pass the new rings before they are properly seated. you will be changing the oil quite often, why waste money on synthetic?
my neighbor is kind of old school. he does alot of stuff on carbed engines, so he puts a gas tank in the air, primes the engine, primes the carb, puts the distributor back on, gets the fire extiinguisher ready and starts 'er up. he then takes it to 2,000 rpms, lets it sit for aobut a minute, then takes it to 4000 rpms for about 20 seconds, then back to 2000... aftera few minutes he'll take it extremely high in the RPMs, lets it drop... lets it "idle" as he re-fills the gas (high idle, at about 15-1700 rpms)... puts it back at 2,000 RPMs, and zip-ties the carb open at 2,000 RPMs and lets it nearly run out of gas. once the tank is low on fuel, he'll kill the motor... (lets it sit at 2,000 RPMs for half an hour or so)
he then changes the oil and filter, re-attaches the proper fuel system, and calls it good to go for soft-driving...
once you've hit 3000 miles, switch to synthetic blend. once youve hit 4000 miles, switch to fully synthetic for the remainder of the motor.
now, keep in mind you are asking for suggestions off the interwebs... you will got alot of "opinion" based comments... my reply to you is my nighbors "opinion" of proper engine break-in.... if you are having this swap done by a shop, be sure to ask them for their process, because if your motor fails and you followed their rules, you will have a better chance of getting retrobution; whereas you'll never get anything from anyone off the internet...