When I change them out, I prefer to use the original length spring as well as the ball bearing detent. The safety just feels more positive to me. I've had folks tell me they used the plunger and spring that were in there with the J-lock safety button and just swapped out the safety button itself, but I'd rather not do it. The parts are about $5 each from Brownells, not that much of a big deal.
lpl/nc