In reply to Wee Davie:
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http://www.pedalforscotland.org/
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> I've just got myself a 2nd hand Specialized Allez which should be faster and easier than the mtb.
> Am I mental to be thinking of doing it?
Not mental at all. You should have the fitness and a road bike will fly compared with the MTB on slicks.
Just make sure you try some decent rides on your new road bike.
Getting your position right, getting your body used to the position for hours at a time and ensuring that the unfamiliar saddle isn't going to tear your arse apart are your main concerns.
The rest of the stuff you may need to know will appear if you search on here for general sportive advice (feeding, pacing etc).