whats the trick for decreasing cid by removing pistons?

[JackD]

Wasnt a Z2 a Japan only 750cc Z1 lookalike?

They are quite common in Japan that has a 750cc limit unless you go to some extraordinary registration length like you might with a HD.
Now a ZX-7 is state of the art for less than $1 per cc.

[Bob E]

You would be much better off swapping the 4b.
Don't quote me on this, it's been a few years since I've been around the B series, none of which where in a dodge pick-um up. But I'm pretty sure the boss for mounting both engines are centered midway respective to engine length. Mounting hardware; bell housing, actual mounts that bolt on to engine, change with the application and a 4b was never put in a ram.
You could simply disable and hold open the valves on two companion cylinders of the 6b. But it will be harder to start and run with a crazy lope. 
Having a custom crank made would probably cost more than a 4b, and you will need a re-ground cam... though I don't think it would be much trouble to swap a 4b injection pump on a 6b block.
 
On a side note there are some Chevy bread trucks running around with Cummins 4bta's and 4btaa's. All the mounting hardware will bolt up in place of a small block Chevy real nice.

[1212FBGS]

to my knowledge,,, you would have to remove the pistons to reduce them from being counted as displacement..
kent

[team_cougar]

It's no biggie for the 4 as opposed to 6 cummins.
If you can't find one, order the blueprint for the engine from Cummins and it will detail the mount locations.
Or, you could just find one (you'll have to anyway to use one) and measure from a static point that both have, like the bellhousing or deck, and pencil it out.

Either way, it shouldn't take much effort to find out.

Also, there are a lot of good diesels out there in the global market that are 4 cyl.

[JackD]

Wasnt a Z2 a Japan only 750cc Z1 lookalike?

Yes Kent
Tax limitartions in Japan limited domestic MC to 750cc.
The Z-2 was the same as the Z-1 with smaller pistons and a shorter stroke.