The later Rancher 55's are all open port, larger 46mm bore, and they upgraded to .375 chain from .325". They really don't have the "ump" for pulling the larger chain or a bar longer than 18", IMHO. I think the "Rancher" 55's were an attempt to steer folks who cut a decent amount of firewood and do some land clearing, etc to go that direction instead of the more expensive Professional models. Must have worked pretty well, you still see a LOT of 55's in service, and Ebay usually has a decent selection to choose from.
The entire series of 55's are very rugged and well made, aside from the weaker direct oil pump drive and plastic intake parts being a few weak spots they are tough little units. Also good parts supply and most of the parts are still available on the IPL's.
The EPA "closed port" 55's are a great find. You either have to know the model years they ran them or be able to see the bottom of the cylinder, simply seeing the compression release and not seeing "Rancher" on the cover isn't enough to ensure you're going to get one. You really need to see the flange on the cylinder, it's lined with a bunch of "X's" across the flange from what I can remember.
The down side to the closed port models is that they were set pretty lean with limiter caps being "EPA" models, and a high percentage of the used ones that show up on Ebay will have some damage across the exhaust side of the P/C.......Cliff