rear ends to choose from?

9" in stock form are not close to a Dana 60 in the strength department. Even the nodular case 9" are lacking without a good pinion support, etc. Factory parts, Dana is better.

Dana 60 weighs about 30# more than a comparable 8.75 rear.

What type of budget are you dealing with? SBP or LBP? Plan on buying new wheels or using your existing?

The axle length isn't a big deal unless you want to use your current wheels. Buying new wheels, find some with proper backspace to accommodate the axle length. Mopar A Bodies have a bit of an issue with the housing end interfering with U bolts if a rear is shortened too much.

Cutting a housing down, get your wheel and tire combo, set them in the wells, measure mount surface to mount surface, and cut to that length.

Moving the perches in using a .75-.80 offset perch kit?

BBP find a 66-67 or 68-70 B body 8.75 rear. They are available pretty complete for anywhere from 100-250 out here in the west. I have a 68-70 B rear, too bad you aren't closer.

My 2 cents stick with a mopar style rear. If you are going to cut something down, starting from scratch, put a Dana 60 under it. It will cost the same to do as a 8.75, maybe less if you get the gears/sure grip in the rear to start with.