lifters

I find that the lifters get noisy on these cars pretty often. I would try cleaning them, there is a little check valve inside each lifter that gets carbon on it and then the valve does not keep the proper pressure and clearance so the lifter 'ticks' away. Most good shops will know how to clean the lifters, it is basically substituting 1 qt of ATF for 1 quart of oil,and letting the car idle for a long time, maybe even an hour. DON'T drive it this way, only let it idle. When the noise goes away, do an oil and filter change. The ATF or automatic transmission fluid has a carbon cleaning additive, I find that it works wonders. Then once this accomplished, run a heavier, fully synthetic oil , like Mobil I , fully synthetic 10-30. It will not carbon up and is heavier which allows the lifters to stay properly pumped up.

Your engine has hydraulic lifters, the oil passages in the lifters small and easily clogged. It is possible a piece of grit or gasket material became dislodged during the previous engine work and has fouled the lifter of the lifter was weak and has just now failed. Try a product called Risolene in the oil and make sure you are using the correct viscosity oil in your engine Too thick an oil will cause lifter noise.