Oh, yes, I know the feeling of boxes of so important stuff which has been with me for longer than my two sons who are in their 30s now. It is almost a part of the family now, and can't bring myself to getting rid of any of it. You probably know the satisfaction you feel when you say I got something that will do in a box, however, it takes ages to find it, and by then you forgot why you wanted it. Still, shows we were keen recyclers even before it was fashionable.
So glad that it's not only me who thinks along those lines. I appreciate the art of mass production and cost per item. But sometimes, sadly more often now, it's just shoddy and poor quality items. There is a smugness beyond compare when you produce something that cost next to nothing and works. I know my kids always say bodge job but funny when they need something at an ungodly hour, and you knock something up how brilliant it is.
I had a look at my cover and it isn't that flat. Pull the bottom bolt up and clamp the top half, mine fits in place and i suspect as the engine gets hot it more than likely will settle in the correct form. Not great I agree, but it might be a case of working with what you got sadly.
From memory, I think mine is a similar shape, but when the bolts are tightened up it pulls to shape. I know this might be a bit obvious, but nip all the bolts in first and then pull them tight. Sometimes if you tighten as you go, it makes it difficult for the item to take the shape up. I will try and search out my spare cover and see what shape that's in.
As I said previously, I had much the same problem and did remove the air box. I quite agree, it really depends on what tools you have and also if it might have been put on by a trained gorilla taking time off from wrenching the wheel nuts up. From memory, I used a ring spanner to release the top nut and through the wheel arch to release the other. I know at the time I though if this is just getting the starter off, god know what It's like to do the cam belt. I gave up trying to get at the nuts and bolts from under, as you say it seems tempting, but I wasted so much time.
If you start the clip at about 1.40 you will see you are not alone.
good luck
I understand that belt changes can be sussesfully done without locking the flywheel, and I have even seen it without the cams being locked as well. Personally, I would learn towards reducing as much stress from the operation as possible and lock both flywheel and cams if I was working solo. Removal of parts and how you access bolts etc is of course personal preference and after the first time as always it becomes less daunting, and you find what suites your method of working best.