SWB Conversion Driveshaft

[cebra]

I have some unique issues with my build as I have limited access to power. With this said, I am doing a SWB conversion in stages. My issue is that once I cut the frame and weld it up I cannot let the truck sit to have the driveshaft cut down (only option is to tow it 20 miles and install driveshaft on the roof of my parking garage). I know where there is a 1968 396/manual trans SWB truck that has a driveshaft. My truck is a 71 350/350 LWB. Does anyone know if this driveshaft would fit once mine has the 12" removed (length/spline/etc)? I have searched a lot and my head is spinning trying to figure this out.

Also related, I am putting in a NV3500 (as soon as I find that unicorn) down the road so if my only option is to cut the DS down now should I convert to 1 piece DS now get it cut down for SWB and then have it cut down again for NV or just have the 2 piece cut down now for SWB and go to 1 piece when I get the longer trans? Thanks.