Read A. Graham Hill's book "Forced Induction Performance Tuning". There are pictures, specs and a good description on the Lancia Delta S4 system. This book is full of good knowledge about forced induction.
The Mercedes M111 variable cam timing keeps the duration constant and advances the intake timing (and valve overlap) with 20 crank degrees from approx. 1200 to 4300 RPM.
tomant
Is your engine model M111 or M271? Dr. Schrick http://www.avl-schrick.com/ had earlier cams for the M111, but now they have only cams for newer 6 and 8 cylinder Mercedes engines. With luck you could find Dr. Schrick cams on ebay.de.
tomant