Yep all 266 are two piece igns. Early 61s are two piece as are 162 and 66. Early Jonsereds 625, 620 and 670 are two piece. All these will fit but all 268, 272 and late Jonsereds are one piece and won't fit. A quick way to tell by just looking is the position of the front left top cover screw and it's relation to the upper left corner recoil screw. If the top cover is forward of the recoil screw it is the two piece ign model and will fit a 266....if the top cover screw is aft of the recoil cover screw it has the one piece ign case half and will not fit.
If you don't mind drilling and taping new holes on the flywheel side the newer style 61,268 and 272 covers will work. That's an old 162. The front has been trimmed to match the case because the newer ones are a little longer.