Same length. There were lots of different types of shock absorbers specified when new - R4, R6, R4F6, smooth road, rough road etc. They all fit but damping characteristics differed. The different characteristics tend to be more for ride quality than safety.
If the current dampers need replacing any of the replacements should be a whole lot better than what you have. If you do drive over rough roads (like my farm track) then the gas pressurised ones are essential for the rear. Any old ones seem to work on the front.