[SSN558]

"easy-to-construct, highly-enriched uranium bomb"

B.S. not that easy to construct. You can't just take a chunk of TNT and whittle it with your pocket knife to the right geometry. Setting it off is an even greater technical obstacle, with timing in the nano second range necessary to achieve critical mass. Amature attempts to make a fision bomb, would result in nothing more than a dirty bomb.

[Tijeras_Slim]

The Little Boy gun-type weapon is a great deal easier to build than the Fat-Man implosion device. The biggest hurdle was enriching the uranium (which is still the problem, unless you can obtain some that is already existant). As far as the design science of the device is concerned, as long as you weren't particularly interested in miniturization of optomizing yield, a reasonable competent physicist could get it to go pop.