DW42 Excuse my ignorance, but what does it mean that it is 27-spline? Isn't that different to the Dana 30 in our 240s? And does it matter (will it fit)?
The Volvo 1030 diff is a close copy of the Dana30, including the 27 splines.
The Volvo 1031 diff is a Dana30 copy that uses a larger pinion and larger crown wheel. It still uses the same axles and same hemisphere.
The only real possible incompatibility is that genuine Danas have two possible lateral locations for the crown wheel, depending on the ratio.
3.64* and numerically higher have the crown wheel in in one location, whereas <3.64 Dana diffs have it moved over to make space for the larger pinion.
Volvo always use the 3.64+ position, regardless of ratio.
*Now that I have typed it out, I am only 93.72% certain that the change is at 3.64. It is definitely around that number.