HO 4-8-4 wheel set swaps

[roundhouse foreman]

My Niagara's have need of replacement connecting bars as they now have very ovaled ends.
These parts are N.A. for the Niagara, nor is the whole wheel set avail.
Will wheel sets from any of the other 4-8-4's swap out?
Is the wheel center spacing the same?
Are the wheel dia's. the same?
Are the bar lengths matching and interchangeable?
Are just the wheel types the difference, spoked vs Scullen?

Thanks

RHF

[RAM]

It looks like all you need is new side rods. 

[roundhouse foreman]

RAM

That is correct, but where are they found?
Not in replacement parts from Bachmann, that is why the question about the wheel sets.
I can scavenge the rods from the set or just replace the wheel set as a whole unit if they are compatible.

RHF