I think the 57 might work without interfering even on the left hand model.
I believe you are right
Sharpsshooter. I just pulled my GPR out of the closet and looked at it. There's no way the Lyman 57 would interfere with the cock. It's a better sight than the TC in that it's a lot easier to adjust and change. It is bulkier though. I have the Lyman on my GPR and the TC on a Hawken. Given the choice, I would go with the Lyman.