1,600 might be about right.
Are we talking 318s or 340s or both?
According to Mike Mueller's "Chrysler Muscle cars, the Ultimate Guide",
Total Rallye production 318 + 340=6865 cars.
Of 6865 total Rallye cars, 1853 had 318s but that means AT and MT.
Of 6865 total Rallye cars, 5012 had 340s.
Of 5012 340 cars, 3769 had AT.
Of 5012 340 cars, 1243 had 4 speeds.
He makes no mention of 3 speed manual transmission, which were an option (I think!) that year nor how many 318s had manual trannies.