Crank Thrusting Foreward Issues

In 1978, I had a low $ fixer upper rebuild on my 383.
By 1980 I had noticed about 1/4 inch forward thrust when blipping the throttle from idle.
You could actually feel it whump forward onto the #3 thrust face.
At about the same time, the mains had worn so you could feel/hear
the crank whip and throb at lower rpm in hot weather. Put in all new mains while in the car one Sunday afternoon.
Crank throb was gone, but only half the crank walk.
Lived with that until I did a full proper rebuild in 1986, and there was a pretty good worn spot on the forged crank to weld up, but smooth as glass.If it's an automatic trans, and you have floating piston pins, fret not.
But it's new, check it out.
Much cheaper before something breaks.