I have two Royal Enfield Bullets, one a proper 1956 trials bike in a Crusader frame and a 1951 Bullet with lots of later Indian parts on it.
My usual green lanes are in the Lakedistrict and the trials version manages all the lanes including Walna Scar without too many problems.
A lot depends on the type of lanes you intend to use, but the main drawbacks are the gearing and the foot rest position. As you have already discovered Hitchcocks you will be aware of the numerous parts available to modify them.
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