TBO's are as follows:
GTSIO-520-H (421B) 1200 hours
GTSIO-520-L (fitted to earlier 421C's) 1600 hours
GTSIO-520-N (fitted to later models 421c) 1600 hours
On UK reg there used to be a restriction on Spars (6400 hours) but not sure if this still applies under EASA. We used to maintain a nice one (N421N) which had been completely refurbed stateside prior to delivery to UK. Had spoilers fitted too to assist with descent. Trailing Link undercarriage makes for smoother landings. Most privately operated don't tend to be on UK reg. If low utilisation and UK reg'd might be worth considering leasing to AOC operator.
The 414's don't have the geared engines.