As others have mentioned, keeping the L20B is the easiest and best way to just enjoy the car and get any other things done - like suspension, brakes, seats, etc.
However, if you can manage a trip down here to Salem, we have a yearly Datsun show/event - Powerland. It's a great way to see all kinds of engines in 510s. Look at the events site on Ratsun to see the past shows. I expect JBirds (the organizer) to be there with his 510 wagon with a V6 and I will have my '72 510 wagon with a VG33 V-6 and carburetor.
Although significantly more work to install, I really like the V6 - and it's 180HP stock. Great daily driver and a blast at the track.
You can see my build thread on the Projects page it's - '72 510 Goon - Prova - because it will be a test
Many details about the swap, and if you don't want to read, there are quite a few pictures because on ratsun everyone loves pictures.
Best of luck with however you go. Post lots of pisc as you can.