I have never disassembled a Lima engine so can say where to look for the oil pressure relief valve, it has one, has to.
The timing belt turns the oil pump gear with AUX shaft for distributor, if so equipped, not sure if the is a reduction gear for oil pump or if it spins 1:1 ratio with timing belt gear.
Common place for relief valve is on the oil pump housing, either part of the pump or the housing the pump bolts to.
The oil pump pumps oil to oil filter housing through one passage, another place for relief valve, I would remove this oil filter housing and check it.
I doubt the filter could be the problem, filters have a by-pass in any case.
I doubt the passages are blocked, i.e. spun bearing, because you are getting "real" higher oil pressure if lifters are causing lost compression, and a blocked passage would still not produce 100psi since relief valve should limit it to 60psi