How hard would it be for someone to narrow a 4th gen aftermarket 9"? Say about 3/4" off of each side. Or how much would it cost to have done?

Couple of reasons why I'm looking into this. 1) There are more used 4th gen 9" rears out there that are for sale 2) I want 4th gen offset(50mm offset) 17x11 wheels tucked in an extra 3/4" and don't want spacers on the rear

 

Depends on what axles are in it. Doesn't matter if you chop off 3/4" or 5", it will probably still need new axles unless you can find someone to cut and respline those aftermarket hardened axles.

To shorten the housing, you should find someone with an alignment jig to make sure the housing doesn't warp when the ends are welded back on.

 

Im kinda a newb... but,

couldnt you pull the axle tubes out of the pumpkin (considering they are pressed in??) Then you could cut off however much you wanted, and press them back in.

Also, I remember seeing an episode of 'Trucks' where they couldnt get custom length axles in time. I think what they did, was get some hefty steel tube, with the same ID as the axle's OD. They cut the axles, grinded the burrs, and slid the 2 halfs back together inside the steel tube. Then welded both ends with a mig welder. The only problem, is I forget how they got the new axles in, with out putting the bearings in first. But I know it can be done.