If you want to lighten up your B4 load here are a few tips...
1) Every top driver uses the plastic chasis so while this chasis weighs more than the graphite it won't matter if you don't have a responsive car. If you are REALLY committed to reducing weight you can cut out battery slots for the chasis which reduces weight and lowers the cg of the buggy. See pic below.
2) Replace steel with Titanium. Depending on the money you have to spend I suggest going with a Lunsford B4 screw set, shock mounts and hingepins. But these hop ups can run you well over $100, you may find knock off titanium screws on eBay but trust me when I say they are CRAP. You can even get titanium CVD's but not sure of their performance. Here is a link
. Also if you aren't using the factory team titanium turnbuckles pick them or the lunsford up.
3) Use everything in the graphite conversion kit except the chasis. Shock towers, arms, battery strap, etc.
4) The RPM parts are actually heavier than the stock parts so if having the lightest possible buggy is your goal you may want to go back to the stock bumper and clear gear cover that comes in the factory kit.
5) Trinity makes lightweight slipper plates for the B4/T4 but there is some debate on whether they are actually lighter or not. Trinity has said they are 5% lighter but on most scales they show up at 6 grams just like the stock slipper plates.
6) Make sure you are using the lightweight outdrives that come with the factory kit.
Hope this helps.