No aftermarket CBE is going to build power with our stock turbo. The stock CBE flows freely for the maximum air flow our KO4 turbo can pump through the engine.
The power gains will come from the DP/RP, which is where the real restrictions are located. It is good that you are going that route. But understand, please understand, that if you are wanting to avoid drone, the DP/RP combo will definitely introduce quite a bit of drone on decel as you pass through the 2500 rpm range.
I ended up putting in a third reso in line in the RP in order to tame the drone.
My humble suggestion is to not go by sound clips on any CBE unless that setup is also running a DP/RP because the latter will definitely change the sound - louder and more drone. So be sure the clips are TBE's.