Sounds like a good swap and interesting. I question the stock datsun transmission strength as well as fitment.
How would you ever adapt that trans to the GM motor??
Has anyone here ever done that?? Maybe its easy..... I dont know.
Also very much understand your strong desire to keep the stock shifter.
Yes anything is possible....
I am willing to go out on a limb here.....That by the time you install the 4.3 engine the fragile custom datsun transmission and driveline angles will most likely change locations drastically.
In short, changing the stock z shifter position you wanted to keep in place to begin with. Requiring a new transmission crossmember anyways, driveshaft length and rear end location adjustments/fabrication to once again get back to proper smooth driveline running angles. So if you are going to go through all of that why not install a GM manual trans. It would be much easier, WAY more dependable and cheaper $$$ in the long run.
I have seen many converted Z's with these transmissions with amazing stock looking consoles and shifters. It's totally possible.