Ok the Z series engine Z18,Z20,Z22 and Z24 are an "industrial" version of the L series engine so bottom ends are pretty much interchangable.

So what you do is get a L20 motor pull the crank rods and pistons out of that get Z22 crank,rods and pistons bore the L20 out so the Z22 pistons fit then bolt the lot in crank rods and pistons then you have an L20 stroker.

You can do the same with a Z24 setup but people have done comparisons between the two setups and pick the Z22 L20 everytime as they give lots of torque but are not as slugish as the Z24 L20.

The reason the Z22 bottom end is used in the L series block with the L series head is the block is a hell of a lot lighter and the L series head is able to flow upto 3 times what a Z series head would ever flow.

The Z series motors come in nissan navaras, urvans and other such commercial or industrial nissan vehicles of the 80's.

Hope ive helped

Jake