Tachi-san, it seems that you have the 289 block and 302 connecting rods are installed. I will suppose then that you also have a 302 crankshaft installed, if possible please measure the stroke (at 3.0" for a 302).
Are the gauges in English or in Italian (and in MPH or KM/H)? Also, is the pulley on the jackshaft for 2 belts (alternator and A/C pump) or does it support a 3rd belt for the pollution smog pump ? Almost certainly your car was not built for the US market (since it does not have pop-up headlights). So it may have been shipped with the 289.
The block you have was used in both hi-po and standard 289 engines, so even if your car was not the Hi-Po engine it very possibly was shipped with the 289 and then someone converted it to 302 displacement.
Very exciting, I think maybe there are only 2 or 3 Mangustas in Japan (including one with a 351 Windsor!)---Lee