Look at the block casting numbers!
This is a series of raised numbers and letters on the block side, ALWAYS with the number “6015” in the middle of it. It might be something like C6DE 6015 A.
First letter is a “C” but it may look like a zero.
Next letter: 6 means a 170 or 200, 8 or 9 means a 188 / 221. There is more to this, but I am keeping it simple for the sake of getting an answer.
To determine if it’s the larger or the smaller possibility take your torch and a spark plug spanner. Remove a spark plug and wing the motor by hand to get that piston up top. If you can see a flat recessed are in the piston, it is the larger capacity. If the piston is totally flat on top, it is the smaller capacity.
The 221 motor is basically a 170/200 block with about 12mm added to the height, same mounts, same length, same width, all of the accessories hook up as original, (fuel lines wiring, exhaust etc) a 170 /200 fan will bolt up at the front without a spacer, no need to shorten anything, a trans cooler is probably not required but can be used, the original trans cooler in your radiator will do the job, (3 core radiator recommend), XP original size. Slight mods to throttle linkages may be required, dead basic once you see it in place. The transmission can be made to bolt up as original in an XP with no modifications if the transmission is from a XR, XT or XW (not XY or later) just fit the extension housing at the rear of the transmission from an XP and hook it up using XP rear cross member and mount. Again if it is the XR, XT, XW box the XP tail shaft will fit. The sump can (but not always) interfere with the steering drag link at full lock, the engine may need to be chocked up 10mm or so the clear this. This is probably the easiest upgrade to do on an early falcon, if you have any mechanical aptitudes and basic tools have a go, the rewards are great, just fit a brake booster to help deal with the extra 20 hp and enjoy, most rego authorities will pass this with out an engineers certificate, as there are no engineering mods and only a very small increase in engine capacity.