Usually a noisy lifter problem is due to low oil pressure, which can be caused by several different things. The most common cause of oil loss to the hydraulic system is a poor fit between the pinion bushing and the pinion shaft.
This engine had multiple problems.
Someone had tried to convert it to a full-flow oiling system, but had forgotten to plug the oil bleed hole at the bottom of the pinion bushing cavity (which allowed most of the oil pressure to leak into the cam chest, instead of pressuring up the rods or lifters). There was also excessive tappet to tappet guide clearance.
Other factors contributing to engine noise – the cam gear was the smaller pitch diameter on the scale, and the pinion gear was the same. Together this created a lot of clicking and clacking, since the gears were not meshed correctly.
The distributor drive gear was aftermarket, and half the teeth were removed for a large cam – which was unnecessary in this engine, and the pitch diameter was also too small.
We replaced the cam shaft and set the pitch diameter (through the color coding process), changed out the distributor drive gear, replaced the hydraulic units, and the roller tappets (for + .005), and reassembled the engine.
It’s now it’s a nice quiet engine with the recommended oil pressures.