Are the spacers different dimensions? I thought it was just the increased spline count and better metallurgy that made the 260z/280z type stronger. Although it's been a long time since I did mine.
I tried getting wheel rear bearings just recently, tried SKF, BSC, CBC and Bursons. All had them available but none had the correct pairings. They were selling mismatched C3 & C4 bearings as kits listed for 240z/260z, OEM and Nissan factory manual list both rear inner/outer as C4 types which have a bigger clearance and therefore higher heat range.
SW Motorsport can get the correct C4 types from Japan.