Is it normal for the lifters push oil out the push rods for 20 to 30 seconds after the motor is shut off???

I have never actually seen this but it seems possible. The lifters get their oil from the pressurized main gallery... if you have pressure in the engine at the time of shutdown it will leak through the bearings and through the lifters until the pressure is down to zero.

20-30 sec does not seem unreasonable...

Thanks Steve

Do your lifters clatter until the oil comes up the pushrods?

Gravity will make hot thin oil run down into the sump when sitting.

I have heard worn engines that had a lot of valve clatter until the oil flowed back into the lifters and made the lifters self-adjusting again. The quietening down of the lifters corresponded with oil pressure rising on the gauge.

Some industrial engines require cranking until oil pressure builds up before they will fire. Or they have a placard directing the operator to do it manually.

I'm really not sure, the Barth is at my son in law's down in Ga. He and his brother are working on it to get it ready for the trip up to Long Island. He and my daughter picked it up at a rv dealer in Alabama for me. They drove 150 miles to their house in Ga. He said it idled rough but smooth out once he got it going. When they started going though it, they found 2 spark plug wires crossed and one spark plug gap completely closed, so it was only running on 5 cylinders. They removed all the smog stuff it wasn't using fixed a couple of vacuum leaks cleaned up and adjusted the carberator. They said after that it ran real good except for the lifters tapping, by the time I got back to them to tell the to try some marval mystery oil in it they already changed out the lifters. They say it's running real good now.
Just have to put new tires on, do the brakes and address some exhaust issues, and it will be ready for me to fly down and drive er back. They are having a hard time locating brake pads any sujestions??? Also does anyone know if a latter model 460 Banks powerpack exhaust system will fit the John Deere chassie. Any help would be much appreciated.