rear axle for F250SD

[nick2015]

I am hoping someone on the panel can help with this question.
I am wanting to buy a back axle for a 99 F250 SD V10 that has a Ratio of 4.30 and a C3 limited slip axle for the back.

I found a salvage yard that has a 2000 Ford Excursion in good shape. The axle number is s415b.
S415-B Excursion '00 4.30 10.50 L - full-float -------------------00 Ford Excursion
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My truck is so rusted I cannot see the axle number but I did find the following on this site concerning axle code.
S421-B Ford F250SD, F350SD Pickup ‘99 4.30 10.50 L - -
S421-C Excursion '00 Ford F250SD, F350SD Pickup ‘99-01 4.30 10.50 L - full-float
S421-E Ford F250SD, F350SD Pickup ‘99-01 4.30 10.50 L - -
S421-F Excursion '00 Ford F250SD, F350SD Pickup ‘99-01 4.30 10.50 L - full-float
S421-H Ford F250SD, F350SD Pickup ‘00-01 4.30 10.50 L - -

The salvage yard states that it will fits my truck. I wish to buy both the front and back axle if it is a match.
I have called the Ford dealership and Ford customer service and they could not help.
Any advice would be greatly appreciated.