Thumper 450 - the intake was noticeable, but not amazingly so, meaning - you're only going to get so much from an intake swap and as far as that goes I'm very happy wiht the Ron Wood kit. I'd recommend it to anyone whoes interested, fit perfect, and is obviously much better than that constrictive rubber boot.
Xcyfz - don't quote me on this, but I'm 90% sure mine is painted steel as well. You can call Elliot at RWR, but i think I have the same intake as you. Only possible diff is that i got the intake kit for the 45mm mikuni carb instead of the 39mm intake. I reasoned that down the road if I step up to their stage III kit which uses a 45mm Mikuni carb, I would need to buy a new intake. Instead i bought the 45mm intake and pushed into the rubber end where it attaches to the carb, a section of the 39mm tubing, effectively eating up the space. I was worried about the lip it crreated, but haven't felt any difference at all. I'm using a power now valve as well, maybe that's helping. Either way, I'm pretty sure I have the same thing as you.