sbka109,
It might be a straight bolt on but with out measuring I can't be positive. But I am sure it can be made to work with some spacers. The good thing is that it has a drum rear brake, too so you won't have to mess with a rear disc conversion.
I just did a quick look at the Yamaha parts break down on bikebandit.com and the Virago 750 and Seca 750 use the same splined drive hub on the rear wheel and the same axle, so it might be a straight bolt up operation.
The Seca 650 Turbo had 18" wheels front and rear and use a straight spoke pattern that, I think, looks better than the swirl wheels on the Virago. I can't tthink of any of the swirl pattern that would have an 18" front.
Ken