1995 BARRETA

If the lifters knock bad then yeah they prollly are bad. Only tip I can give u is that if ur going to go through the trouble to replace them. Replace all of them. Not just the ones that are bad. If ur just fixing to sell. Then its ur choice really

what color is the smoke? If its black u prolly have a fuel problem. Ie, need new fuel filter, need injecters cleaned, prolly need whole fuel system cleaned (which requires a trip to the shop). If its white or blueish, ur prollly burning oil and that could be from a number of things including blown headgasket. If ur going ot replace the lifters ur going to end up replacing the gaskets too so that might fix ur prob. If it smells sweet its an antifreeze leak.
Keep checking on all the levels for all the fluids while ur working on this. Last thing u prolly need is the engine to freeze from no oil, or over heat from no antifreeze. Also check ground to see if any fluids are leaking onto ground. Kinda gives u a rough idea on where they are leaking

Also, while your replacing the lifters, go ahead and replace the valve seals. Oil may be leaking past these into the cylinders causing blue smoke at start-up.