First prototype completed 100 days after the contract signed. In contrast it took decades to build the Eurofighter. Granted a more complex aircraft, but they didn't have CAD back then either.
Mustang vs Eurofighter isn't really a fair comparison in a number of ways.
The most important, I think, is that Mustang wasn't a government project, but one designed and built by a private company to meet an existing wartime need.
Eurofighter by contrast was a government job start to finish, built by three companies in three countries. Starting with a DNA like that delays and cost overruns are baked into the process.
https://secure.wikimedia.org/wikipedia/en/wiki/North_America...
First prototype completed 100 days after the contract signed. In contrast it took decades to build the Eurofighter. Granted a more complex aircraft, but they didn't have CAD back then either.