Forget Black Widow or Sandy Spares (same thing) headers for the Gen 1. They cause nasty flat spots just where you don't need them and no amount of carb work will alter that. It's due to the (lack of) design and R&D in the header lengths etc.
Muzzy were the only manufacturer to come up with a set of EXUP-less headers for the Gen 1 that gave top end gains without sacrificing anything low down. That said, their peak power gains weren't as high as Akrapovic or Yoshimura, so you pays yer money etc.
Your SP can will work OK with the stock jetting and you might gain a little more power at peak rpm. If it's a shorter can, though, you might lose a little in the low-mid range but the extra noise will probably hide this by making it at least sound more powerful.
I would hold off fitting a performance air filter until you've rejetted. The extra air they allow in might just tip the balance of the fuelling to point where a marginal lean mixture could show up in the throttle response and part-throttle cruise.