Possibly, you might want to check around for a 3.50 that has a more modern tread so it would be a closer match. Avon makes the AM26 in 100/90-18 that is the same height as a 3.50 but it's wider so there could be clearence problems with it.
Sorry if I missed this, but does the larger diameter in front affect by much the accuracy of the speedometer? I would think it would be more accurate with the larger wheel. Truth?