Good work. How do you trigger the timing light - with a low voltage signal or with a high voltage? For the later, one could use a GM HEI module to drive a coil, and clamp over the HV spark lead as the timing light is normally used. A VR type crank sensor can trigger an HEI module. A round-about way, but with all off-the-shelf parts (have in my garage).

Reading between the lines of the M-B instructions, it appears their processing box times the delay between the TDC pulse and the RI pulse, and converts to crank angles. It seems you could just flash the timing light at the crank marks to verify it flashes at 15 deg ATDC. It appears that the RI pulse does not align with "start of delivery". Perhaps it marks TDC of the #1 IP piston.