Good on ya for rigging an inexpensive tool.
Regarding "V clamp with a bolt tightener are usually too big and cumbersome to fit a Mercedes". I've had quite good luck using the A-Frame on all three of my vehicles.
Under what situation did you have a challenge with the A-Frame? Not looking for an arguement. Just a chance to pick up another data point.
S, J.R. Brown
2000 G500 LWB Obsedian Black
2005 Toyota Tacoma Access Cab Off Road Sport
1993 Volvo 240 Sedan Anthracite
1980 450SEL Champange (owned it for 15 years. Great car)
1986 280GE LWB Anthracite (Sold it and kinda wish I hadn't)