Disagree on the wildly over-engineered. Father worked both at Los Alamos and Hanford (where I am today) and didn’t ever suggest that was the case. The implosion-type devices received only minor changes in the next few versions.
Well, you could use the W87 as a benchmark.
Yield ~20 time Fat Man. Weight ~1/20th Fat Man. Twelve of them, independently targetable, fit on one Peacekeeper missile. Obviously, there were major improvements over the years!
If you want to go to the other extreme, there was Tsar Bomba, aka Big Ivan. It weighed 30 tons and yielded 58 megatons. Once, in 1961. Over Novaya Zemlya. The fireball was five miles wide. Biggest gadget ever.
A Boeing 777 Freighter has a revenue payload capacity of 112 tons.
Of course, if your plan is to ship a gadget to the infidels, a standard intermodal container would likely be a better choice. No missing PAX. No angry ChiComs. Just a big anonymous box, with a maximum gross weight sufficient to accommodate Tsar Bomba.