Panels normally are 6ft. I repaired a fence for a friend recently
where they had used metal posts cemented in. It wasn't hard removing
the rotten fence posts out of the old metal posts with a hammer and
old screwdriver and a few minutes patience. However the posts had been
placed in tight - about an inch less than 6ft. I just removed the last
batten on the panel, trimmed the top and bottom battens an inch and
nailed back in (screwing is even better). Used a saw to trim the
overhanging feather edge panels and job done.