Thanks. Yep I have left the bottom angulars free of rivets on the end. Will fit counter sunk. My frame is sprung and the top is at least 30 mm away from the fire wall. Within reason the cabin and engine mount seem to mount on the top firewall where they like give or 10 mm. Be nice if this was pre drilled. I will have a go at it. Probably easier than it looks when I actually do it.
Thanks Lyndon