If you are planning to create a family heirloom with your truck, I would restore it to original "with safety upgrades". I had done something similar with my 51. I replaced the tired 235 that came with the truck with a rebuilt 261. For fun, I put dual intake and exhaust on it. I after having fun with the truck and wearing out the pinion bearing, I rebuilt the rear end with a 3:55 kit. I left the SM420 transmission alone.
As for safety upgrades, I installed lap belts (3), radial tires, and the second tail light with turn signals.
Now I can have my kids (2 are now 7, one is only 1) hop in my truck with me and go anywhere.
Its fun to look at the pictures of the kids growing up with this truck.....
