South Downs way over two days? I've never done it.
Did it in 1989, first big mountain bike ride I ever did! We did it from the traditional start near Petersfield (80 miles).
That time we stayed at the Youth Hostel that is (was)? right on the route, conveniently at the half way point.
We also dumped the car at Eastbourne, then went by train to Havant and rode up to the SDW. Don't suppose you can do that these days as they still had guards vans back then and I'm sure there's not enough trains at the right time etc
1991 Cannondale SM1000
2004 Specialized Epic Comp Disc