[lolife99]

The disc conversion itself will widen the front track width.
(thats why the 71-72 rearends got wider when they introduced disc brakes in 1971)
Crossmember are the same width.

I always use to use disc brake conversion hoses from ECE also.
But member Ledd Zepp cross referenced those hoses to find out they are just '78 camaro hoses, that can be purchased MUCH cheaper at your local auto parts store.

The only oem part that I would use from a donor crossmember would be the backing plate/dust shields that go behind the rotor. But they can be purchased new also.
Or like some,... that don't run them at all.
DIsc conversion spindles (drop or stock height) can be purchased for around $230.
FInd someone that offers free shipping and you will be set.
I cringe when I hear people buy used, wore out crossmember assemblies for $100-$300.
But then again,... they are probably the ones that install them as is.