Remote Reservoir Ohlins for 1979 CR 250 - 417mm - This is from a 1979 issue spec sheet
Piggyback Ohlins for 1980-82 CR250 - 445mm - and that is from a 2007 issue spec sheet
Just one other point, when your measuring up old shocks to fit a bike, check that they are assembled correctly first. I had a pair of Husqvarna Ohlins from around 80-82 and when i pulled them apart i found that they were put together all wrong and someone had moved the seal head down lower in the body to either the second or 3rd groove to make the shock shorter. This also ment that the wiper was floating around loosly and not pressed against the o-ring in the gold cap. There are proper ways to shorten them rather than doing what the person did with the ones i have.