The boxy version was produced from either 1982 or 1983 and lasted until about 2000, when the rounder M250A2 was started. The M-250R2 always had a round profile though.
The original boxy M250A2 (originally known as the M150) came out in the early 80s and was made until '87 or '88 when this pictured model came out, then in '99 the current rounded model came out.