Spyntec is owned by Solid Axle Industries.
Spyntec Conversions - Spyntec Industries LLC. I just talked to Steve down there about two weeks ago, and ordered some monster Jeep hubs to fix my Dad's basher... . He has the best ABS setup of all the axle conversions I've seen. They are not exposed to the elements like the factory or Dynatrac versions.
I've sold Dynatrac products for over ten years, and they are a top notch company to deal with in my experiences. I ordered an axle, two sets of floating hub kits, and several gear sets since the first of the year, and not had a second's trouble..... I'm surprised to hear you're having problems..... I'd think they'd be quick to do you right... .
Solid Axle's kits are not cheap by any means. I don't think anyone has a "cheap" kit. I've had some issues with EMS when they first got started. Apparently they didn't want to sell me kits as a dealer, so they never returned my calls..... No big problem, as I can do business elsewhere, and have. Solid Axle also offers dually kits with their free-spin kits, something other's don't offer. If you order a kit from Dynatrac, you'll have to order a set of dually adapters to go with 'em from someone else, like Arrow Machine. The SpynTecs are machined from Chromolly, which is an inherently tough material, and rusts much slower than other materials, such as cast iron. They often take heat much better than other units, and are definetly less prone to stress cracks. That material is very similar to what we use for rifle barrels in the firearms industry, repeatedly taking a 60,000psi pounding every round... ...

For the money, I think they're the best currently available on the market. Inner axle shafts are available from other sources, but may be available from them, too. You'd just have to check with them to see.
I don't believe the Yukon Gear Spin Free sets offer the larger inner axles with their kits, either. If you order them from Randy's Ring and Pinion, you can get the axles included with your order. From what I've seen, these kits don't offer as much for the same price.....
Any of these kits are far better than the factory unitized kits available. Also, check around on TDR, there are some build-yourself kits from Ford parts that can be done fairly reasonable, and I think would be a good upgrade, too.
one such thread, very good read... .
https://www.turbodieselregister.com...nsmission-discussions/226856-whoa-nellie.html