Cutting up a rear axle.

All 8.75 rears should be 30 spline axle, truck or car. Haven't seen 35 spline side gears for an 8.75. You can spool it and get an 8.75 to 35 spline.

That 55" housing is likely a B body housing if it 55" for just the housing, see below. If it's total width, wheel mount to wheel mount, then it's something different.

Dana's in cars ran 23 and 35 spline depending on years with Power lock or trak-lok sure grips. Trucks came with all sorts of spline counts, 16, 23, 30, 35.

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'66 B-body 54 1/4" housing, 59 3/8" axle flange to flange, 44" perch 23 spline power-lock sure-grip, 1330 U-bolt yoke

'67 B-body 54 1/4" housing, 59 3/8" axle flange to flange, 44" perch 23 spline power-lock sure-grip, 1330 strap yoke

'68-'69 B-body 54 15/16" housing, 60 1/16" axle flange to flange, 44" perch, 23 spline power-lock sure-grip, 7290 yoke

'70 B-body 54 15/16" housing, 60 1/16" axle flange to flange, 44" perch, 35 spline power-lock sure-grip, 7290 yoke

'71-'72 B-body 57 7/8" housing, 63" axle flange to flange, 47.3" perch, 35 spline track-lock sure-grip, 7290 yoke

'70 E-body 56 31/64" housing, 61 5/8" axle flange to flange, 46" perch, 35 spline power-lock sure-grip, 7290 yoke

'71 E-body 56 31/64" housing, 61 5/8" axle flange to flange, 46" perch, 35 spline track-lock sure-grip, 7290 yoke