Well, I used a couple quarts of this stuff to break in a new flat tappet solid lifter 440, as part of a hobo stew of oil I had in my garage.
I used a couple 50wt racing, five 10-30 diesel, and some Lucas additive. Probably too much zddp looking back..... but the purple shaft broke in beautifully.
@S'cuder , do you remember the zddp level in the GT50?