http://www.osengines.com/engines/dimension-metric.html
http://www.jettengineering.com/ Click on "Jett Engines" on the left side of the page. Then ".40 through .65L" in the middle of the page. Then "Click Here For Engine Dimensions" about half way down in the middle.
Well... the short answer is I don't know. While I own about 50 OSs, I don't own a Jett .50. Possibly the links above will allow you to compare the dimensions and answer your own question. I don't have the time right now to do the analysis on the engines but maybe you could post what you find. I would pay particular attention to the dimension that locates the spinner. My guess is that most of the dimensions are close enough but if one motor is longer than the other you may have a goofy looking gap at the front.
Bill
Edited to remove table and formating... too confusing...