1987 F-150 XLT 4x4

He said knocking.

I know of one 1976 F100 4.9L that knocked rather loud for over 40K miles
until I bought the truck and changed the oil & filter,
I put 4 cans of "thick" STP Oil Treatment and straight 60W racing oil in it.
It idled for 10-15 minutes "thumping" until a piston rod came through the lower block.
And of course, this engine never ran again.

If an engine isn't smoking,
new Sleeves/Main Bearings can be installed on the crankshaft to give an old engine a longer life before a full-rebuild or replacement.
Some will say: If you go that far, rebuild it!
And that is one way to look at it.

Again, you may want to consider a 20W50 oil change,
so the main bearings pump-up quicker or get quieter sooner.

KNOCK is wear...