This is the basic one
1.
http://www.summitracing.com/parts/FMS-M-4210-A/
Cover Bolts 10
Ring Gear Bolts 10
Pinion Spline Count 30
Ring Gear Rotation Standard
Cover Gasket Included Yes
Pinion Shims Included Yes
Carrier Shims Included Yes
Crush Sleeve Included Yes
Pinion Seal Included Yes
Pinion Nut Included Yes
Ring Gear Bolts Included Yes
Head Bearing Included No
Tail Bearing Included No
Carrier Bearings Included No
Axle Seals Included No
Axle Bearings Included No
Next step up
2.
http://www.summitracing.com/parts/FMS-M-4210-B/
Cover Bolts 10
Ring Gear Bolts 10
Pinion Spline Count 30
Ring Gear Rotation Standard
Cover Gasket Included Yes
Pinion Shims Included Yes
Carrier Shims Included Yes
Crush Sleeve Included Yes
Pinion Seal Included Yes
Pinion Nut Included Yes
Ring Gear Bolts Included Yes
Head Bearing Included Yes
Tail Bearing Included Yes
Carrier Bearings Included Yes
Axle Seals Included No
Axle Bearings Included No
3.
http://www.summitracing.com/parts/FMS-M-4210-C/
Cover Bolts 10
Ring Gear Bolts 10
Pinion Spline Count 30
Ring Gear Rotation Standard
Cover Gasket Included Yes
Pinion Shims Included Yes
Carrier Shims Included Yes
Crush Sleeve Included Yes
Pinion Seal Included Yes
Pinion Nut Included Yes
Ring Gear Bolts Included Yes
Head Bearing Included Yes
Tail Bearing Included Yes
Carrier Bearings Included Yes
Axle Seals Included Yes
Axle Bearings Included Yes
I highlighted what's different between them in Bold.