I am about 180-cm and I played Hooker, what I used to do in the scrums for hooker the ball would be to twist my body slightly so my feet are sideways also having long legs help, I found it was easier to scoop the ball back this way, well used to win more scrums than lose them, also if it was a power scrum you were going for its very easy to get dragged along as your arms are pretty much stuck, so leg strength I find is a must so work on that as you will be pushing a lot with the legs without the traction of using your arms to pull against, I also found with my feet slightly turned I used to be able to get more foot into the ground to help with pushing in the scrum.
The linouts I found was much much easier to throw in one handed I really dont get why players these days throw them two handed I find it makes it much harder and more prone to going a different direction in the air.