always the safe way to do it. dont want to glaze the cylinder walls. you could ask your builder. some factory motors come with synthetic as the factory fill, having been built for it. i have heard of some builders building the motor for it, but you would know (and have had to ask for it, i would certainly think).
i would let it go for 5K to be safe. make sure you do lots of changes with dino oil early on - get the metal out of there (i know you know this, but someone probably doesnt). good luck and enjoy!