I agree with Liberoz, 20-30 hrs is way too unrealistic IMO.
From word 'go' push the button on the stop watch then see how long it takes to get the car back on the road driving AWD. Picture lifting the car up, removing the wheels, rear suspension, exhaust, cutting out the floorpan of the donor vehicle (if not already done so), carefully cutting out the floorpan of your own car, doing the captive plates, aligning and jigging up the new locations, double checking by fitting parts before fully welding, welded floor and subframe mount in, grind back welds, seal the welds etc, paint in chassis paint, bolt rear end all done, diff in, bleed bakes, add fluids, fit fuel tank and suspension etc back in. Then do the same for the centre tailshaft mount,.. align, tack into place, check, weld in, paint, fit exhaust. Then connect the transfer case, the tailshaft to the transfer case and fit front driveshafts. You cant argue that there's definitely a lot more than 20-30 hours there easy