Best not to over complicate it.
I use a 1x10 board leaned on a 6x6 block of wood.
I do them with bodyweight for high reps between sets of deadlifts.
I wouldn't want to do them weighted, not a very stable position for your feet.
Not to be a negative nancy or anything.....but I don't really see how a set up like this is anything more than complication for the sake of complication. If your rectus femoris needs more work, hit some sissy squats or leg extensions.