Forget the Scarpa boots, and invest in a comfortable pair of trainers, if your feet have motion control issues, then seek trainers with maximum cushioning and support.
I believe the London to Brighton route, if its exactly the same route as used by the vintage cars, then its all on road and tarmac.
62miles is a very long way, and the right footwear is vital for enjoyment and hopefully success on such a long challenge walk.
If the weather is warm and dry, which it can be in May, then you need your feet to be able to breathe, and remove as much road heat as possible.
Both those are impossible in boots, so high quality trainers that provide maximum cushioning to your feet and ankles, combined with very high quality socks.
1000m socks would be ideal, as their twin skinned, and provide the best comfort and support from inevitable blisters.
Years ago, i did venture past the 100k or 62miles distance, on several occasions, but never totally on a hard unforgiving surface.
If your still unsure, try walking 20miles in a pair of Scarpa boots, i can guarantee you will not enjoy the experience.
Boots are designed for off road, mountain terrain, and hitting the concrete for mile after mile, in cumbersome boots, is not advisable.
Remember your planning to walk a double marathon, plus another ten miles.
Good supporting trainers would be the best footwear for a demanding solid tarmac route, as your feet will enjoy the comfort, and your legs will not be carrying so much weight.
Take my word for it, once your body ventures past 40+miles on any terrain, fatigue sets in, and the more cumbersome your equipment, especially your footwear, the more tired you will become.
My last big challenge back in 1999, resulted in me pulling out at 78miles, totally spent, and i can remember the damn ruck sac and boots felt like lumps of concrete on your body.