The J4 suffix indicates the unit is equipped with a universal power transformer. Inside a terminal strip allows the unit to be switched between 100, 120, 200, 220,& 240 voltage sources. Sequential numbering for the 2270 started at 1000, so you have the 52,219 unit manufactured (minus -999). They made a total of 84,484 units. Remove the top cover and inside by the tuning string, stamped on the aluminum bar usually on the right, you will find the date of manufacture.
Here's the date on my 2325, March 9, 1976.
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