Unless the floorpan in the Nova is already bad I'd have to vote with the guys who suggest going with a subframe conversion.
The S-10 conversion would work but you are still going to have to build a complete floorboard system and body support system.
As far as tread width I don't think that they are that far off. The early Novas are pretty narrow themselves.
Here is a site that you can make good use of http://www.novaresource.org/dimensions.htm#1963
If my old eyes are reading that white print right stock tread width is 56.3 Inches.