datsunfan1963,
I should get all the parts from the donor truck\engine (including drive shaft)
Yes, this would be the preferred method and based upon the condition of another 320 you could chose which one is in better overall condition to get in driving order.
Your other option of locating and purchasing individual parts will get expensive over time and a big "if" is can you locate and purchase every essential part necessary to change your 320 back to a column shift - I would venture to say no - sorry.
A few unknowns to consider are the fabrications made to your present 320's frame for A14 engine and transmission mounts. Again, cost of repairs here can be costly to fabricate new frame mounting points for the engine and repairs to the cross member where the transmission/rear engine mounts bolt on.
The A14 is a good motor , probably has a few more horse, and ready available tune up parts. So you might consider keeping the A14 in place and enjoy the 320 while you try to source the necessary parts or locate a donor 320.
Hope that helps and does not dampen your motivation.
Li'l Truckie