Oilit
Cruisin' on my Bluebird
That's definitely a Murray built frame. There was no Cruiser 5 in '83, so it should indeed be an '84 model. What is the 4-digit number stamped in the headbadge? That will indicate the day the bike was built, which is much more accurate for dating a bike than the serial number as that only indicates when the headtube was stamped before it was even welded into a frame.
The serial number starts with JU (September 1983) and the head badge stamp is 0184, which would be the 18th day of 1984 by my understanding, so you're right, it's a 1984, no question.