It's good that you are using the bar only to break in the GM'ings. For an extra light stretch, try putting your toes on a 2X4, or such. You will feel it much more in the ham's and calves. Might also have the feet wider apart for better balance. Two hundred lbs is not out of the question before long, if you wish.. You will find as you advance a slight knee bend is required for balance and to counter act to the heavier weight. Guy's who get into extra heavy weight of 350+ only preform a quarter rep, or so, with a half way knee bend. Seen some guy's near or over the 400lb mark do GM'ings that resemble a quarter squat. Hard to tell the difference, really.
If anybody ask, the GM'ing is not like, or the same as, doing SLDL's. The muscle curve/physics are different. One has the weight in front of the body. The other above and with-in or behind the natural line of the body. Neither is better than the other, just different body responses. Might want to alternate both movements in a workout program, from time to time. Both exercise can help the squat and regular DL greatly. Good Luck.