If you are installing a different block and still have the old block, yes, you can just transfer over the plug. The easiest way is when the pan is off the old block. You can drive the plug out with a punch and just hammer it into the new block. If the pan is still on the old block, either pull the pan, or, work the plug out like I explained in my previous post. If you don't have a factory plug, you can get one from any pickup or van that has a slant 6 engine. They both used a dip stick tube that went directly into the pan. It shouldn't be too hard to make one either. I'd use brass or aluminum, but, even a wooden dowel would probably work ok.
