Welcome to the forum
Whilst I appreciate you are in Canade, I've attached the link to the MCA Rescue Boat Code which talks about self righting. I don't think there is a prescribed requirement for how it is attached - it just needs to hold the bag in place. The lacing method seems to be a good way of attaching it to the A frame at the back.
The righting bag works by making the vessel unstable whilst it is upside down. The vertical distance between the centre of the righting bag and the centre of gravity of the boat is a key factor in this. I'm a bit surprised that it would be possible to achieve this with a righting bag in the engine box. There is also the added complexity of ensuring it can deploy from within the box as there is the risk that it may get trapped in the box.
https://assets.publishing.service.go...e_-_Tagged.pdf