That's a pretty nice kit but reinforced rockers? Here's what you need.
"Champion" HD Shaft Rockers for GX200 & 212cc 6.5hp Clones — Vegas Carts & Performance
Great advice you can't beat those champion rockers. They are a bargain, and give accurate non flexing valve motion but you must check and set the geometry for best results. I don't like either of those cams for the folowing reasons.
1) rattlesnake is reground no hardfacing or hardening otherwise very similar to the black mamba Jr. just less lift.
2) 252 0607 Is for higher rpm and some head mods.
Can you specify if you are needing mid range torque or Hi rpm horsepower?
I would think a Isky Black Mamba Junior would be a great wide powerband cam for great midrange and still make some power up to 7K.
I have a big valve head I just took off my old kart motor. Cleaned it up, touched up the seat, it had 26LB springs and new alloy retainers. you could have cheap but it's a 32mm intake and to work well would need at least 350 lift to take advantage of the big valve so it really wouldn't work well with your build and would require ratio rockers like the gage ones (expensive).