I just took an eyeball measurement on my 3W24. It looks like the header extends about 2.5" out from the centerline, and the can at the rear extends out further.
I think you should go for a twin, won't cost you mucch more than a new 3W24. RCShowcase is selling the RCS44 B2 for $475 right now and mufflers for $70.00, that is a neat little twin and would look great on that Rascall. I have one of these, but have not had a chance to run it yet.
DKjens