Have to agree about not trying for weight loss. You could lose a bit by eating sensibly but keep up the Carb intake till after the ride.
On the training- No need to go overboard on milage. Just do quality rides. 30 milers where you push a bit harder than comfortable will do- Take in a few 15% hills on a similar length ride. If no real hills available- Sprint up 1/2mile slopes as interval training. Then take a good milage ride for 4 hour nonstop if possible to get the butt attuned.
Get out on the bike but don't over do it. Just get out and enjoy yourself and enjoy the ride
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How long was I in the army? Five foot seven.
Spike Milligan