408 SB versus BB 541

The "No Replacement for Displacement" guys will be all over me for saying this, but don't get too hung up on cubic inches. Heck, even Top Fuelers only run 496-500 cubes. Different animal, yes; but proves it's not the end-all beat-all.
The Porsche is what, a 3.6L? So you're going to build a 541 c.i. motor to try to beat a 220 c.i. motor that probably cost more than 10 times what your build cost? Sorry, no glory to be had there, especially if you're still not into the 10s.
Stick with the 408 and get it healthy. Work on your suspension, get it to HOOK and LAUNCH. All the displacement in the world ain't worth hooey if you can't put it down- and you don't have the kind of rear weight bias that German torpedo has, and a big block will exaggerate that even more. A well-sorted stock-appearing suspension gets you into the mid 11s in the FAST series, so a more aggressive suspension without their limitations and a well-tuned 408 could do the trick; and if you want to be sure, give it a shot of happy gas.