The Gen 1 drive is actually the first drive in the Alpha series and was standard equipment from 1983 until the release of the Gen 2 in 1990. The Gen 1 also replaces most of the pre-alpha drives from 1977 to 1983.
There are actually 2 versions of the Gen1 - the R and the MR. This does not matter when purchasing a complete drive or lower unit. All the GEN 1 drives available today are the latest MR version.
In 1996 there was a small change in the available ratios due to new gear designs. So the current available gear ratios are:
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