You said you had low oil pressure, what is the PSI?
I suspect he either installed the wrong lifters or installed longer pushrods.
Does he have the part numbers of the parts he used? If the vehicle is louder then it was then I suspect he installed longer pushrods which will keep the valves slightly open and you may have the exhaust valve hanging open during the combustion or it is opening quicker on the cam lobe.
Let's start with this and go from there.
I attached the part number for the lifters below. Let's make sure they are correct.
Image (Click to make bigger)
Wednesday, April 28th, 2021 AT 10:15 AM