Randy,

for what it's worth, the old Rossi and new NovaRossi will have the same mount pattern spacing (25 mm) and width (52 mm if memory serves). However, the crankcase length of each engine is different with the current NR's being a fair bit more compact than its other Italian predecessors.

If you are using a glass engine mount, you can swap engines by simply using two identical mounts and locating the NR further forward on the beams, or, perhaps better yet, making some 1/8" ply spacers for the engine mount when using the NR and just use the same mount.

It might be a bit of a moot point as the NR will be immeasurably more impressive than the vintage Rossi - despite Cesare being at the helm in the design of each...

David