From your confused response re; 1.6 rockers, just use the 1.5 rockers. They are just fine.
If you want it to really scream get some L-31 vortec heads and a vortec style 4 bbl intake manifold for your 400.
Big big difference in "truck power and torque
" from stock 400 SBC heads.
the stock 400 heads are lame. Now the cam can work.
Don't forget to hang on