You bloody ripper Tony, this ended up being the key. Tried again last night and got the bar engaged into the radiator on the first go!

Before starting I gave all the surfaces of the fork that touch the radiator rubbers a light smear of grease, it all slid together so much easier with no catching on the rubber.
The other thing I did different was not lifting the jack/crash bar as high. Previously I would have the bar forks centered in the lock panel slot, then try to lift the rad up to the correct height to match with my "spare" hand. This time I came in at the bottom of the slot, lined up to where the radiator had slumped down to.

Oh, and I cheated a little in a moment of frustration the previous night. The "closed in" fork of the crash bar got opened up & de-burred with an angle grinder to match the other side which meant I could get one side fully seated before moving on to the other, rather than having to engage both simultaneously.
It's still critical to keep the forks level front to back as they go into the rubbers though.

Clips - easy side was relatively easy. Removing the MAF pipe gave loads of access. Again, grease any part of the clip that will come into contact with the rubber. The metal clip must be on the plastic part as you install it. Took a lot of force to get it engaged all the way in and not much hard stuff to lever against so I threaded a thin piece of rope around the back of the clip and through the lock panel then leant my body weight back on the rope ends to seat the clip.

Hopefully the rope trick helps on the hard side too.... When I find the damn clip. Spent a good bit of time looking now and still can't find the second plastic bit. I have got the metal bit at least.

 

Great success!
I ended up pulling the bar out slightly so the clip would clear the AC pipes and came in from the wheel well.
I had trouble getting the inside to clip in first, so did the outside then used a long flat head screwdriver seated on the inside of the clip, quick tap with a hammer and it seems to be locked in.



Thanks for all the help!