keep the steel/metal scrap and sell for scrap IMO
There's no reason you shouldn't be able to fit that thing in a 40 yarder unless its full of crap. IMO
Would add an allowance for a second smaller dumpster if needed so he is aware of your concern. If not then on the final bill just cross it off if you didn't end up needing it.
Dumpsters are pretty cheap up here so we always add an extra or two in case depending on the job.
Also depending on the company you use they either won't care if you overload them, we used a different company on a house demo and they bitched even if they were over just a tiny bit. Other company we use now (and only them) get it done lol, they picked up a 40 yarder with a triaxle and the front axle came off the ground as he left shifting through 1st and 2nd and 3rd. Guy didn't really care though so it was awesome!
That E50 looks nice!