how do set the timing in a international 345 gas engine?

Answer 1

On mine, I just pulled the vacuum line off the advance on the distributor and plugged it. Then used a timing light and set the timing. I can't remember, but I think it was something like 6 deg BTDC. Then locked down the distributor and reconnected the vacuum advance line. That's all.

Answer 2

For IHC 266/304/345/392 v8's time off Cylinder 8 (spark plug wire on passenger side at back of engine).
For smog California engines are timed at 6deg BTC, and Federal (non-emissions) are timed at 0deg (with the vacuum adv. disconnected and idle set at 650-800 rpm
Most of these IHC engines actually run best at around 12deg BTC.