McCullough has described Alonso as “super motivated” upon his winter arrival from Alpine, with the two-time Formula 1 champion displaying an early level of determination that is driving forward Aston Martin.
From last year's post-season test in Abu Dhabi, McCullough concedes the primary focus from his perspective has been on getting Alonso up to speed as quickly as possible.
In that regard, the 41-year-old is putting in the time and the effort, starting with the sim, as he embraces his latest new working environment.
“When you have a new driver you get his input, and that's what we've spent most of the winter really doing,” said McCullough to invited media, including Speedcafe.com.
“It's still going on. Fernando spent four hours in the simulator ahead of everything else he was doing (for the launch).
“That's the sort of push we are getting from him. He's massively motivated, pushing us all really hard because he wants to do really well, just like we do.”
‘No wasted words' with Alonso
After watching Alonso over the years, McCullough is now effectively realising an ambition of working with the Spanish driver.
McCullough is fully aware of Alonso's reputation for proving difficult when the tide turns against him.
That was witnessed last season when he became irritated by Alpine's lack of reliability which undermined his season and played a key role in his exit.
But McCullough is ready to embrace whatever Alonso throws his way.
Detailing the most striking aspect of working with Alonso so far, McCullough said: “Fernando is very engaging, very focused, and he is very efficient with how he talks as well.
“So when he's describing the car, when he's describing the way he thinks a report should be written, a configuration on the steering wheel, there are no wasted words.
“It's just focus, focus, this is what we should be doing, this is my idea. He's super motivated.
Alonso like ‘an extra engineer'
“I've always really fancied working with him from the outside. You see stuff from the outside, and obviously, he's been challenging at times.
“But his performance on track has obviously been phenomenal throughout his career, whatever car he's had.
“The number of times that you've been racing against him, even when he's not had as good a car, and he is just a pain – week in week out.
“Qualifying well, racing well, you listen to him on the radio, and he's all over the strategy of the car, in front of him, behind him, what they're doing with their tyres, where he is relative to them.
“So it's been great fun getting to see some of that.
“But I'm really looking forward to seeing him in a qualifying and race situation because he's like an extra, very experienced good engineer but someone who is so fiercely driven and competitive.”