Welcome and thanks for your question. My name is XXXXX XXXXX X am here to try and assist your with your question
good morning Steve and thanks for your time
If it is just a signal lifter noise on one side of the engine then you have a bad lifter. To verify the oil pressure is ok and the oil pump is ok then preform a oil pressure test. If you have oil pressure then the oil pump is good. Buy what you typed you have a bad lifter.
is it a easy job to replace??
I have never worked on a Mitsu before Nissan yes
You will need to remove the valve cover and the intake manifold.
That is better then the oil pump with the timing to worry about
I want to thank you for your advise and you have been very helpful in this