engineer
The 450 rear wheel is a narrower width rim.
But , the brake shoe is the same as the Savage . So really the 450 is the easier way to go . You just slip the Savage brake right into the 450 hub and it fits !
On the pulley side , the mounting bolts for the chain sprocket are on a smaller dia. circle.
I have 1981 wheels (1 set 450) and (1 set 550) they have different spoke patterns.
The 550 has the same sprocket as the 450 does so :
I had to slot the mounting holes in the (belt) pulley to let the mounting bolts through. Its aluminum and easy to do. Getting the pulley centered was easy too , just measure the gap and make/find a spacer to fit.

The front is even easier : just 1/4 inch spacer on the calipier mount , and your done !
I've got about $100. in my 450 set if your interested ? plus shipping. I looked at Daves post about rims and tires for the Cafe Bikes is why I went with the 550's , Shinko makes a 110/90-16 that would be just fine on the 450 rim - it took a lot of "Doing" to make that 110/90-16 grab on the wide 550 rim and blow up to seating. But I already had the tire on hand so .....