To give an idea, i purchased mine 12/07 from Hobby Barn reportedly as "new" shipment from the UK. Yet it was manufactured in Jan/Feb 07. I do not know what to make of that, but maybe it's a reflection they do not make many SP series. They may have in fact corrected the muffler issue by now, but there's only one way to find out - ask.
I never owned a tach before getting my RCV, but took the proper break-in of it very seriously and got one for that purpose. It cannot be properly done without one, as specific the procedure is with needle settings etc. For one you can't get an exact reading on your idle needle, as the specific difference needed with glow connected/disconnected is impossible to accurately tell by sound. Bill at BJ's has a great tip sheet for RCV setup, and being very specific regarding rpms and needles doing it minus a tach is not reliable. I'd highly recommend you buy or borrow one.
RCV has excellent service, so contact them and i'm sure they'll solve your problem. But be prepared for a scolding trying to break in their engine properly without a tach...
Good luck to you -