I have 62+ ft. clearance and and 'just' make it under the bridge at south end of the Alligator-Pungo canal. This bridge 'may' be 63-64 above Mean High water - suggest you direct contact the USCG (Eliz. City???) for the 'actual' clearance .... its NOT a 65ft. bridge clearance !!!!!!!
Ive seen several 64ft tall boats unable to pass this bridge ... especially when there is slight 'wind tide' in the canal.
BTW dont anchor in the Alligator River anywhere south of the bridge at the Albemarle until you go west to enter the Alligator-Pungo. Most of the bottom is foul with sunken logs. If you do anchor on the Alligator R. be sure to have a trip line attached.
6'8" deep isnt going get you through the dismal .... they continually drag for sunken logs to only 6 ft. deep. .... and if a large powerboat precedes you he most certainly 'disturb' the logs. DEFINITELY dont travel the Dismal Swamp route is you have a 'sail drive' and that goes for 'any' depth boat.