Fallows was recruited from Red Bull Racing, where he had been one of Adrian Newey's key lieutenants for many years, and began work at the Silverstone team in April.
Inevitably, that has led to pointed suggestions from the Red Bull camp that the very competitive AMR23 is a copy of its car.
However, McCullough says that Fallows and new head of aerodynamics Eric Blandin were keen to mix their own knowledge, gained at Red Bull and Mercedes respectively, with that of the existing team members.
As such, they've encouraged the team to pursue an "Aston Martin way" of approaching car development.
"One had been at Red Bull one, the other than Mercedes," said McCullough of Fallows and Blandin.
"They very much wanted to do what Dan refers to as the Aston Martin way, which is let's listen to everything, let's listen to all the people internally, let's get the input from the two different ways of developing a car and then look at where we need to improve, and look at what we think is the best way of doing that.
"So that's one thing I think Dan's been very good at, just saying you've always got to look at what other people are doing – but you've got to do it your own way, if you want to try and beat them.
"That's been Dan and Eric's sort of mantra from the beginning, from an aerodynamic and concept side of things. That's the reality, which is why the cars do look quite different, if you look at a lot of the areas of the car."
McCullough stressed that Fallows, Blandin and other new recruits integrated well with the team in 2022, with chief technical officer Andrew Green – who has now moved off the F1 project – playing a key role.
"This year's car throughout last year was very much under Andrew Green's leadership," he said. "So he was getting Dan and Eric up to speed from a performance development and aero development side of things.
"They've largely been I think very happy with what they've seen, the tools, the people. We were onto a path even before those guys turned up, but they've just brought another level of experience and knowledge from two of the best teams, Mercedes and Red Bull.
"They just brought a lot of understanding and experience from there that has just helped evolve how we work, and that relentless push.
"I think a lot of it is about creating that atmosphere to give that creative thinking which Dan and Eric have been very keen to do from the beginning.
"They've been quite happy with the ideas and the information that's come from even existing people, and been really happy with the level of what they've had to work with. So I think that's been good.
"That leadership in that direction, and that competitiveness, and that drive is what Eric and Dan have really brought to the party."
McCullough said that the difficult 2023 season had helped to bring the team together.
"Last year we developed two ways," he noted. "We'd gone a certain way, it wasn't the right way, we accepted that, we changed that, they then arrived during that process.
"And they agreed and then took hold of that and sort of ran with it. So I think the working relationship between Dan and Eric and Andrew Green last year, plus the other the senior people, has been really strong.
"I think in a way when you're not too competitive, and we know where you're trying to head, it helps bring people together a bit. And that's what we had last year. We were all disappointed when we weren't fast enough at the start of the year.
"And Eric and Dan as well as being very competent are very good people, they're really decent human beings, and they really want this project to work. So it's actually really easy and fun to work with them."
