J8 is just neutral lens. With two choices. White, which could be from fifties and black, which are up to nineties. Blacks have more modern rendering and easy to shim.
J3 is character lens at f1.5 and also better lens at f5.6. After trying of all pre-asph Crons, 1.5 Norton, Planar ... I prefer J3. Black version also exist, but it is next to white elephant.
I'm fine with J3 from fifties. It is very good on bw films and OK on digital M.
But I know how to shim them. If it is not shim, then soft stories are made.