Single-leg sled pushes and pulls involve emphasizing one leg to move the sled on each step, which is especially good if you're trying to focus on a weaker side.
An easy way to implement these single-leg sled push and pull variations is to simply perform half the distance or duration with one leg and do the second half with the other leg.
I'm thinking about great, big triceps. Triceps so thick that you'd have to rest them on a desk or chair to keep them from tiring your shoulders and elbows. What did these old-school guys do to get them?