Thanks for the comments and advice guys, will give that a go!
Dave, I cut the tail in stages:
-First masked the upper vertical with the trusty insul (electrical) tape, and cut evenly from both sides with the razor saw.
-Next masked the main vertical, and cut in same fashion as above, but to just a little under half thickness - needed to retain a semi rigid joint to prevent stress on the horizontal section while cutting (felt this would have been harder to cut with long vertical at full thickness).
-To cut the horizontal, all masking tape was removed, and worked both sides evenly with the craftknife* (again to just under half thickness).
(*will use the scalpal in future rather than the craftknife, as Wojtek suggested - thinner blade)
-Then continued carefully (and evenly) working this and the long vertical section together till completely seperated, using razorsaw in the long cuts and craftknife at the junctions. Cleaned up with the flat file to finish.
(Any advice on a better way of achieving this would be appreciated, as I have other similar projects
)
Next stages to be tackled: hollowing out of the rudder hinge areas, tail wheel well, elevator control bar cutout (aft of the tailplanes), and tail access panel, followed by some interior detailing... this will not be quick....