Thanks for the feedback guys.
So, I did take all the plastic off to get at the rad cap, (wish I hadn't) and yes I left the 2 screws out on one of the front panels. Thank you fartmarty.
Since that is solved, my final question is what bolt goes here? The bolt that I thought went there is too short, its not grabbing, unless the rubber grommet has backed off?
Good thing I don't do this for a living.
Lastly, I'll pass this along in case it helps someone. I didn't want to take the coolant reservoir off to drain it out, or pull the lines; but I did have a turkey baster and tube which worked beautifully to suck the remaining coolant out and also was perfect to top up the rad when done.