Hey there Scott...… Basically the 220 and 250 were alike, with the most obvious exception, the NH220 has external fuel lines (go into Google images and look at the "intake" side and you will see fuel lines running from the fuel pump into external fittings in the heads. When you type in NH250 you'll notice the fuel lines are not running "thru" the heads, but rather run "inside" of the heads to feed the individual cylinders). They used (basically) the same other components (but as you stated, there were many variations). Hope that helps brother....
Look forward to seeing your build!!!
DJ