Beginning at the Sir Chris Hoy Velodrome in Glasgow, the ride will go through Ayrshire to Glenbuck, the birthplace of Shankly, and continue to Carlisle United where the former Liverpool boss made his first appearance.
It will then extend to Preston North End and visit the Shankly Kop, and then down through Merseyside past the hallowed turf of Anfield to finish at Liverpool's famous Pier Head.
On Friday, Fowler and Harkness visited Dolan Bikes in Ormskirk - who have produced bikes for elite stars including Mark Cavendish and Bradley Wiggins - to customise their ride and pick up training equipment.
"I'm getting pretty nervous!" Fowler told Liverpoolfc.com. "It's all for a good cause, trying to raise money and it coincides with Bill Shankly's 100th birthday.
"It's massive for everyone, we all know how much he has done for Liverpool. The more people on this bike ride the merrier as far as I'm concerned.
"He means a lot to the club - he's synonymous with Liverpool. For us to be involved in anything remotely Bill Shankly and Liverpool is fantastic.
"I think there will be a few people really looking forward to it. It's not going to be easy to cycle 270 miles, albeit in three days, so it'll be tough. We'll egg each other on; there will be no competition whatsoever.
"For any person wanting to get involved, it will be fantastic.
"Myself and the Foundation are setting up a JustGiving page. We're going to try to raise as much money as we can for charity. That will be available soon on my Twitter page, @robbie9fowler."
Fans can participate in the event too, with 150 places available for the complete journey; alternatively, a further 300 people can elect to experience the final 33 miles from Preston to Liverpool.
Harkness added: "Robbie asked me to come on it so I'll have a go and see what it's like. I obviously had a bike as a kid but since I've been older I've never had one.
"We'll probably have a race now and then for a bit of fun, but I would have thought we'll take it easy - it's going to be a long, hard ride.
"As well as the charity, we're remembering Shankly and what he did for the club. The places we're going to are clubs he has been to, so I think there will be a lot of interest."
After talking the pair through the requirements of a cycling challenge of this size and passing on his words of wisdom, Terry Dolan explained why the most crucial preparation is in the mind.
"The hardest part about that is just thinking about it because they are top athletes and they'll soon get back into it," he said.
"They know how to get in peak condition so I'm sure they'll be able to manage 70 miles a day. They know all about training.
"It's a community-based project that's worthwhile doing. Because it's local as well, to me it's very important. It would be nice to see 300 cyclists riding down Scotland Road.
"I'm sure a lot of people will do it because a lot of people have got a lot of respect for Shankly and what Liverpool have done for the city over the years."