and this says

For 1965 the Comet received updated styling front and rear (including stacked headlights). The base 6-cylinder engine was increased from 170 cid to 200 cid. Still using a single-barrel carburetor it produced 120 horsepower (89 kW) at 4400 rpm. The base 8-cylinder engine was increased from 260 to 289 cid and, using a 2-barrel carburetor, it produced 200 horsepower (150 kW) at 4400 rpm. The standard transmission continued as a column-shifted 3-speed manual transmission. However, the optional automatic was changed to a "Merc-O-Matic" 3-speed automatic transmission (essentially a Ford C4 transmission).

So different sources have the 289 appearing one model year later. I am not a Comet guy -- just passing on what I found.