Welcome Kimsey.
Is this the 'Against Breast Cancer' 60 miler from Harwell?
If so, it starts out fairly flattish and at the half way mark near White horse hill gets a tad lumpy and rolls on occasions back through Wantage to Harwell. It's a cracking route on a nice day (and it's OK in a downpour too). It's not as lumpy as L2B and there's a lot less people to contend with. It's also worth realising that there are fewer rest-stops too, so you might want to carry a bit of emergency food to keep you going just in case.
As stated, keep building up the miles and time on the bike, if you can get out 2 to 3 times per week even for say a short 10 mile loop it's all good training. After a few weeks try say a 20 or 25 miler. Few weeks more try to get a 40 in etc. To be honest once you're up to about 40 miles, the rest is about fuelling and getting used to time sat on a bike. If you can do 40, then 60's not a big leap,if you can do 60 then 100 not far behind.
Eat before you're hungry, drink before you're thirsty. That's the rule.
Start gently and pace yourself, be economic on rolling ground, don't waste energy fighting hills, take them gently. Keep rests short.
I'll be there god willing with the NOBS fat-boy team in our new Logo'd team shirts with the Against Breast Cancer charity logo as well (it's our team charity). Some of us are doing the 30 and the 60 plus the ride form Abingdon to the start and back to make it a 100 miler day out!
Oh, one final bit of advice, if you can find a riding buddy to train with, that's great motivation... you'll progress faster.
Cheers
FF.
BTW, whate are you riding and where are you based?
.I was recovered by the next day,,but would like to be better prepared for this one! 
