This reminds me a little of the debate often had about common hull forms for ships. The argument basically goes "build every type of similar ship using the same hullform - it will be oodles cheaper and everything" - even if the hullform in question is a couple of decades old. A variation on the theme is "why not just build "new" Type 23s, instead of spending all that money on a Type 26?"
While ships and aircraft are (obviously) very different, a couple of things have parallels.
1. The external shape of the ship or aircraft is important to performance, but is only one part of the design. Internal weight distribution, component loading, system functions are equally, if not more important.
2. The actual ship or aircraft is manufactured from literally hundreds of thousands of design drawings, detailing components, assembly etc.
What I think Jim is trying to demonstrate (and I agree) is that it's not just a question of picking up a set of drawings (assuming a complete set even exists) and programming them into some super whizzy computer thing that will magically churn them out in the blink of an eye and for the price of a pint. In the interval, many things change, which may not be apparent. I have little or no knowledge of aircraft design regs, but would have expected that there are many changes in what you can and can't do with materials from a design, manufacture and assembly PoV compared to previous practice, say thirty years ago. I would also expect design performance standards to have changed as well. On a ship for example, one of the reasons that T45 and T26 are so much bigger than their predecessors has very little to do with big radars at height and everything to do with regulations on accommodation standards, escape and evacuation routes, fire protection, damaged stability, etc etc.
A long list of changes, against which some may say "good enough for my day, good enough for now". Maybe, maybe not. Accommodation standards don't have a direct parallel with aircraft per se, but safety does - particularly since the decision to forego Crown Immunity. All of those things dictate that every system in a ship or an aircraft must be assessed for safety against current regulations which in many cases means starting from scratch and going down to component level. It is these sorts of design exercise that may not have ever been considered in great detail in previous ships or aircraft and the cause of much angst in the "airworthiness" argument. Just determining which organisation would be the design authority (and whether they would accept that responsibility!) would be a major exercise - look at what VTTST have had to do for XH558 just to fly a constrained envelope for civvy displays.
Just one other aspect is the availability of equivalent components, which is one of the arguments against building a "new" batch of T23 for example - I'd bet good money that one would have to go through the materials list of pretty much every drawing and change the requisition number of the majority of component parts - simply because you can no longer buy them new. That takes a phenomenal amount of design effort and cost as well - and that's before you consider the cost of translating paper-based drawings into contemporary CADAM format that can be used on modern computer systems.
There are many other examples, but conscious I've written an essay, I'll leave it there and hope it demonstrates why a new-build V-bomber is not easy or cheap. What should be absolutely clear is that it ain't survivable and it's unlikely to be certain, unless you build either an LO version (even more different design requirements) or hundreds of them (costly to build and man). For a deterrent survivability and certainty are essential for credibility.