I would be a little leary of using a sealer until I knew that it needed it on your parts, if it was one of the early Mopar heads and block I would say you have to use sealer in them. Maybe not needed on the new casting like you have, do you know if the block has wet or dry sleeves? if wet use the sealer now before it leaks into the oil, if dry I would run it first before adding any sealer, no sense in taking a chance of clogging up any coolant passages