To quote from my webpage
https://people.physics.anu.edu.au/~amh110/Handling/volvo_sports_handling_V2.htm
FRONT STRUT TUBE ASSEMBLY UPGRADE:
For performance driving and motorsport, the 1982-on struts feature a larger diameter stub axle and are recommended over earlier 240 model years. How to identify: Stub diameter for the outer bearing (the Small one) increased from Ø19 to Ø22 and the inner bearing (the Big one) from Ø31.8 to Ø35 - the transition diameter from stub axle to strut body (the most important dimension for strength) increased from Ø42 to Ø45 - therefore all changes feature a diametrical increase of 3 mm. The 82-on strut tube also features a reduced inside pipe/tube diameter, meaning the strut insert is a lot tighter fit compared to earlier versions.
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So, the direct answer to your question is the hubs (the brake disc mounts to the hub) are different as the bearing(s) are bigger. A matching part to the newer strut.
Same wheel studs though.
Anthony