c30 front suspension question

[Plastic Mechanic]

Hello all.
I'm building a 61 c30 DRW, and I'm swapping to a 73+ front end to gain power steering and better brakes. (also swapping rears)

I found (but have not looked at) a 75 c30 single rear wheel parts truck with obviously, a SRW style front end.

My question is, how are these front ends different?

Is it only a spacer that makes up the difference in width, and are they commonly available?

Also, would a 75 SRW tonner likely be equipped with a 14 bolt, or Dana rear?

Thanks,
Eric