Appreciate the insight there Ross.
I think pre-drilled backing plate is a good idea, with some heavy duty washers and bolts with loctite to finish off. I'm hoping like hell that it will be as easy as lining up the 3 holes, securing, and off we go. I'll try that and process of elimination from there as may need second hand set up (may have smashed it to bits inside the door who knows, although from what I can feel is intact apart from wobbling around because not secured with the three bolts to subframe),
or something of the like. Again appreciate feedback and will update after I look on Saturday morning. Cheers.