Spline count difference is only in the center shafts of the axles into the different CV’s used in the Demon/RE axles, the spline count and size of the splines that go into the Diff and wheel hubs are the same on all, yes they will fit.
I’m not a fan of DSS Axles, gone through 2 sets of them already. If your going to spend big bucks on axles spend a bit more and get GForce Outlaw axles or find RE take offs. If they can take the shock load of a Demon pulling the front wheels off the ground they’ll take most anything you can hook them with on the street and most likely the track too unless you have a 15” conversion and making 1100+ wheel.Why not just get DSS axles? And a stock rear? With the brace and possibly an AAD rear suspension upgrade to square it all up, I would think you should be plenty fine
Actual metal bits or metallic film on the drain plug magnet?I’ve changed the diff oil every year to be safe. This time there’s metal in the oil. Not sure if it’s the diff or from the axles splines taking a beating so I’ll be changing both.