Hi Tim,
I did some checking on the net and I could only find the Rancher 55cc. I don't think that the 50 was sold here. Here is a web site for parts and the Rancher 55 parts are cheap. http://www.jackssmallengines.com/husqp55r.cfm I think that the cylinders me be interchangable. If this is the case you could get the extra displacement in the bargin. The cylinder is flange mounted to the top half of the crank case or the whole case is part of the saw body, which has to be cut out of the body. Also I have seen many Rancher 55 saws in running condition on Ebay at very reasonable prices.

I hope this helps, Dave