In Phil Larder's 'Rugby League Coacing Manual' (published around 1990) he states that you should never sprint/plyo etc. on the same day as performing any leg work in the gym.
What an incredible post, holy cow where do I send the check! That looks like a great workout, the propping situation is one where as a 35 (almost 36) year old second row (wanna be 8-man) I either have to take up tennis or play prop and be quiet. Since I want to play I must prepare myself for the impact. The Good Mornings should work perfect for this.
I have played 7's in the past, and am actually pretty decent, I have played on several representative sides. But my body is wearing down and I need to rest.
The question James asks is on my mind as well, I have always heard not to sprint and lift on the same day. This was mainly from coaches who probably did not know, they were simply repeating what they heard.