You really have no clue how a nuclear weapon works do you?
Given the numerous posts here, I do know how it works. What is clear is that you clearly don't have a clue.
You only need about 40lbs of HEU, which is the step they are at now.
Incorrect. The step they are at is about 1,000 + lbs of LEU, which as Arch pointed out can be made into a weapon by excessive use of neutron deflectors and shaped charges. The problem with that is largely weight.
You clearly don't understand the difference between LEU and HEU and what they both entail in producing a weapon.
they either reconfigure their known plants or they have something set up elsewhere... take 4-6 months max to process what they have.
Perhaps, but it makes more sense to produce HEU from the start rather then making LEU and then enriching it into HEU which is longer, more costly and less in line with a weapons production facility. If you had any understanding of history, you'd know that both the US and Britain had dedicated facilities specifically designed to churn out weapons grade material. That ain't Iran.
And fatman was bulky because of the era... we didn't know better... explosives were different
Hardly. Fatman is fundamentally no different then what Iran is doing aside from being plutonium rather then uranium based. And explosives weren't difference. The same principles for shaped charged and neutron deflectors are the same as today abet with better milling processes. To produce a weapon from LEU would require huge amounts of additional shaped charges and deflectors, all adding additional weight.
Like I said, Iran's going to need a semitruck to deliver such a weapon.
a fission bomb is at the heart of every one of our modern nuclear weapons... it don't take much set one off.
That's because our weapons are fusion based and fusion does not occur at room temperature. A fission reaction is required to produce the correct level of temperature to allow fusion to occur. Iran is
not building a fusion weapon.
Do you really think it's much secret how that thing works?
You do realize that weapon was more or less suicide for whoever used it no? Furthermore, the yield on such a weapon was absolutely tiny compared to what we have today. Not to mention that the weapon was an implosion type. Being a single millimeter off in a shape charge will cause the weapon to fail. It's quite a feat of engineering that we actually managed to build such a small implosion type weapon in the first place.
And using that you could attempt a multistage fusion weapon....
Come again? You think that a .1 kiloton blast could produce the necessary heat to sustain a fusion reaction from large amounts of HEU?
MAYBE. But it's real questionable that such a small fission reaction will produce sufficient neutrons among other radiation necessary to cause fusion.