I'm not familiar with 240s... but I will definitely concur. The earlier dana/spicer 27 units as found on mid-late '60s Volvos have the 10 spline axles, and limited slip units can be had. Still hard to find though, but gear lockers can be bought new for about $275. But not really appropriate for a street car. Those rears were never installed in wagons though... they went straight from the Salisbury unit to the dana 30, the change between '66 and '67.

That oddball 10 spline axle dana 30 though is a whole different ball of wax. the limited slip unit ptional, but expensive as original. Most commonly found in 123GT models, which are rare in and of themselves. The absolute best option is to find one of them elusive disc brake 1800 rears, and make it fit to suit. Thats my plan with my '66 wagon. and the posi option is the only reason. I could care less about rear discs.

The 4wd shops I called told me the dana 30 was easily identifiable in that the axle stubs are not exposed. But the later drum brake Volvos DO have exposed axle shafts as we know. They are, to the best of my knowledge, unique to Volvo. And only for those few years.

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-Matt '70 145s, '65 1800s, '66 122s wagon, others inc. '53 XK120 FHC