As Michael said `not to difficult to replicate` with less $ than genuine. Unfortunately the end result will never be a CSL.
It is sacrilege to tamper with an icon like the CSL.
The better approach is to extend on the stock M3 with mods that will equal and surpass a genuine CSL.
i.e 3.4/3.5 stroker,S62 or S85 powerplant with upgraded susp/brakes.
As a sidenote the different engines from the `00 era that are used to repower the E46 M3 are:
(S62 torque vs S54 torque makes for the best street mod/bang for buck.
The S54 engine in the E46 M3 is rated at 343 hp (DIN) or 333 hp (SAE) at 7,900 rpm and 262 lb/ft of torque at 4,900 rpm.
The CSL-spec S54 engine is rated at 360 hp (DIN) at 7,900 rpm and 273 lb-ft of torque at 4,300 rpm.
The E46 GTR 3,997-cc dry-sump motor produces 380 hp (DIN) at 7,000 rpm and 288 lb-ft of torque at 4,500 rpm.
The S62 engine produces 400 hp (DIN) or 394 hp (SAE) at 6,600 rpm and 369 lb/ft of torque at 3,800 rpm
The S65 B40 is rated at 420 hp (DIN) / 414 hp (SAE) @ 8,300 rpm and 295 lb-ft of torque @ 3,900 rpm.
The S85 V10 is rated at 507 hp (DIN) / 500 hp (SAE) @ 7,750 rpm and 383 lb-ft of torque @ 6,100 rpm.