open clone valve size and additional parts

I just got a clone to tun in the open class on my kart it ran pretty good against the two strokes on the small track but they still beat me so I need a little more power. its a blue clone std bore and stroke + .020 rod flat top piston raceseng s1 flywheel 14cc head ported with stock valves it has a dyno 265 cam and bored carb on alcohol. Im already looking for a tillotson alcohol carb and planning on getting a 315 lift 260 duration cam with champion rockers. and dual valve springs. but my question is I would like to get ss valves but being a std bore and stroke should I get stock sixe 27/25 28/25 28.5/25? I will be putting the stock carb back on sometimes to run the stock appearing class looking to twist around 8000 :scooter:
27mm intake is about the biggest you can go unless you go to a bigger seat for it. you also need to open the bowl to take advantage of the larger valve. 28.5 and 25 is a good combo for that build.
If you're just wanting to knock off a few friends with what you got, I'd just change my gearing, upgrade the clutch, and upgrade the valve train
this is competitive kart racing at many differnt tracks i have the tires, good set up, proper gearing, built 2 disc bully clutch running a micron 4 tach i can twist 7300 im just lacking in the hp
should i get the 356 lift 254.3 duration dyno cam or the mod1 310 lift 247.6 dyno cam or the 315 260 isky or the 330 260 isky or the 360 260 isky? lots of choices but its for a race go kart looking to twist 8,000 and what about block venting should i do one from the valve cover and one from the block to a catch can?
The Isky 310 cam, is good, Dynos 308, or NR's 307, are all nice up top cams for twisting high rpms...

The Black Mamba sr is nothing to sneeze at either it will pull past 8000rpms then some.