Rear can easily be shortened, just replace the tube. Any local prop place can do that and wouldnt cost that much extra compared to shortening/welding/rebalancing anyway

Are you using the 8.8" in the car ?

A 1 piece shaft could be viable as long as you wont see shaft speeds in the chart, or stepped up diameter, or went to alloy or composite.

That will depend on wheel/tyre combo, diff ratio and road speeds you may see. And of course if you have room for the 1 piece with the axle motion up/down before it hits the bodywork.

But retaining 2 piece and altering a shaft you have can make most sense, as less parts to buy.