hi mate,
that's one nice Z. I just went through that kinda pain in the not distant past...
in regards to your oil filter block. if the stock rb30 threaded screw on fitting is there, you might want to measure the exact diameter on it, then check the block sleeve.
My first motor failed because I left the 30 one on, which is a beez dick too small for the sleeve, and oil does not circulate properly, and caused the same failure that you have suffered.
if you do have the rb30 one on the block, you need to get another one, or rb25 one which has the thicker sleeve.