If your A1 is anything like mine, I don't think needle length is too much of a priority. The needle is held in a clamp, and can be moved up and down to achieve the correct position before tightening the clamping screw. According to the manual, ''The needle is fixed in the needle bar, with the long groove toward the operator. Near the top of the needle bar is a line across it. Turn the machine until this line is level with the top of the machine head. With the machine in this position the middle of the eye of the needle should be level with the top of the throat plate.''
So long as the needle is long enough to fit in the clamp with the eye in the correct position, I guess the only critical measurement would be the distance between the eye of the needle and the point. When I bought my machine, it came with 90-odd needles, which were a complete hotch-potch of sizes and manufacturers; I've swapped and changed needles without any problems.