Ok if you really want to do this 100 per cent correct you would use fswr ( flexible steel wire rope) between your 2 tow points of the car and use an equalising sheave. Using a shackle as a runner is ok but it is a way of doing it without the correct gear. Also if you opt to do it the correct way you will truly equalise your load between your 2 points and also need to make sure your sheave is correct for the fswr you are using... I can go into all the minimum requirements of sheaves and fswr but don't have time right this minute...
Scotty
P.s the information I am providing is through 18 years of rigging and open ticket crane operator ( currently sitting in a 280 tonne crane lifting 80 tonne concrete footings using equalising gear....
